I realise the following may not be the best way about things....but it worked for me (6 years ago) and has never reverted since....

I had almost exactly the same situation/s with my M.I.L!
I had a (premeditated) cranky hissy fit at her one day and layed down the law. Which of course was not pretty.
The next day I appologised for the WAY things were said the day before, but explained I was glad the issues were aired now. I said I was glad she now was aware of how I felt about the issues although the way I went about it was not probably not acceptable, I did MEAN what I said,  but I was feeling particularly pre-menstrual (or P.N.D.ish if this better suits your situation) and let it get away from me. I appologised again, and, yes, things were a little awkward for a few weeks afterward as she found her new boundaries, but we get on great now, and if she is unsure of the "boundaries" with the kids or our house (or even hubby) she now asks first. We also made the rule "Her house - her rules" " OUR house -OUR rules" (within reason of course - consistancy is always the best guide with all kids) for the kids which gives her some of her wanted "powers" with in our family.

I think someone else mentioned taking it until you get the one you want - and making that clear.  You never know, in the future it could be really handy for a spare room in a bigger house, or for one of your kids.  You could use it as storage in the garage, or refinish it more to your taste.

Though, I get the feeling that this isn't just about an entertainment unit... Some inlaws are so nice that it feels as if you are being Smothered.  To me that means their Son is being mothered, they just have to look after their little boy (regardless of his age), and you are an extension of him now.  I am sure it is well meaning, and honestly, if you are too adamant in your refusal, you will look like the 'baddie' - speaking from experience.  Your mum in law may well get upset as she is only trying to help... The kind of things boys appreciate and girls find interfering.

Have lunch with your hubby and inlaws, tell them that you are overwhelmed by the amazing way they try to help you all the time, however you hope they don't mind if you make some decisions for yourself.  Tell them that it isn't because you don't appreciate their help, you just feel that you need to grow and make some independent decisions with your husband as you don't want to be a burden to them.  (This counteracts the 'we only want to help' from them).  By doing it casually over lunch, with everyone involved, it means that there is misunderstanding as all parties are present.  If the conversation gets out of hand, back down for the time being, and let sink in slowly by repeating it next time a similar issue arises. 

Maybe when your inlaws started out, they wished that someone had helped them in this way, or maybe they just can't let go... Whatever the reason, it doesn't seem malicious, so tread carefully - but firmly.

Have you tried asking her for some of her recipies or cooking advice. Sounds to me like she may be trying a little too hard not to be the wicked mother in law. Let her know that you can't wait to try out her recipies. You never know , you may pick-up some great tips & make a great friend, after all you have alot in common. Your Partner.

There isn't really any nice way as she'll take all personally anyway. Just be straight forward with her as you need to set an example for your own kids. If you continue to allow her to do everything then your kids will think it will be ok to rely on other people to do everything for them. Make your partner speak to his mother aswell. Good luck with this.

I know how much of a nuisance it can be, but sometimes it can be good accepting peoples offers until you get a bit of financial stability behind yourself in order to be able to buy the lovely things you want for your house, and still be able to cope with paying bills etc. Its what i did a while back when i bought my house!
As for the cooking, as far as i am concerned, even though other people have enough on their plate, if they offer, take them up! Settling in to a new house and unpacking things and arranging them can be hard work, especially if you have children... which i see by your photo that you do!
Just let you MIL know however that you appreciate all that she is doing for you, and once you have settled in to the house, you will return the favour in some way or another!
I hope i have helped you!

firstly i want to say to everyone thats replied, great advice. when you do end up getting the entertainment unit that you want, why not put the black one in ur bedroom for a smaller tv just to save arguments? and as for the cooking, if theres one thing ive learnt, (not with my current MIL as she is great, but my past ones have been horrors, when asking cooking questions, only ask the one. TRUST ME!!!!  any more than one and you will look like you are incapable of looking after her son and she will think far less of you. honestly. i wouldnt say that unless I meant that. any other cooking questions, ASK ME!!!  or any other close friend you have that isnt close to your MIL.

good luck ppl.

Hi
Take the wall unit use it til you have  the one you want.
Then I am sure you have a friend somewhere that is in need of a wall unit for their place
We never say no to second hand furniture clothes anything.......
We have lots of avenues for distribution to other needy people.....

As for the food issue be grateful she wants to help....have you got room in your freezer to freeze some of it for a night when you don't feel like cooking
Wish someone would bring a whole pile of food over for us.....would save us a fortune
Just my thoughts
Luv Deb

I'd do anything to have a helpful mother-in-law rather than a next to useless mother-in-law but, on the same token, interference is interference.  Seriously, put aside the black (probably gold trimmed) entertainment unit and the daily offerings of good food (cause let's face it, she has no faith in your cooking) - isn't the fact that your mother-in-law is coming over EVERY day into your home and taking over your role as a wife and mother.  I think you need to be firm and so does your husband in setting some boundaries.  Do it now because the longer the situation goes on, the worse it will get.  Good luck and let us know how it goes.

You say you already have in mind what you want in your house, which suggests to me that you don't have it yet!!
So accept the offer graciously, use it until you get what you really want, and then ask them what they would like you to do with it as it no longer fits into your house.

As for the second question,  this is one for your other half to fix. He needs to tell Mum (frequently) what a good cook you are (presume you are ) and then invite them over one night for a meal, don't try to out do her with exotic stuff, even, God forbid, ask her advice about a couple of things, but overall prove to her that you are quite capable of looking after her "little boy"

You could say that black isnt really what you wanted and maybe if you took it to the second hand shop they may want it. as with the meal issue when she comes over next let her know that you are dying to try the new kitchen and you prommised hubby you would cook, or simular. good luck, I know what it is like to have a tooooo helpful MIL.