Well I can tell you my current build I have, that even though I"m replacing, I'm only replacing it for gaming purposes. Other than that, It runs flawless.
1. 8 Gigs of DDR 2. 4 would prob be ok, If your only doing the Movies, and tabb'ed browsing. Ram is rather cheap though now a days, and it would be worth the extra 30 bucks.
2. ATI 5750, or Nvidia Equal. Haven't had any problems out of either brand windows wise.
3. Gigabyte 965-S3 is what I have. Though I don't think you can buy them anymore, Newegg.com - Computer Hardware, Motherboards, Intel Motherboards, LGA 775
has some with the 775 intel process chip. You can even buy a board that runs DDR 3 for more performance but again, for what your doing, its not needed.
4. Intel E6400 Duo core processor. Base clocked, it runs at 2.13 Ghz, and is easily Overclockable, if your into that kinda think to 3.2 air cooled with the right aftermarket cooling. I run mine at 2.8 ghz on stock cooling and voltage just fine.
5. 5.1 Sound is built into the Motherboard, but any Decent sound card would do, if you have to have one. I've always used the built in one, and has never given me a problem.
6. Spend the money on a decent blue ray player/dvd writer combo. http://www.newegg.com/Product/Produc...82E16827135247
comes to mind though out of stock atm.
One thing I would recommend, is Paying decent money for a video card and disabling the onboard video. You'll save more hair in the end.
It just depends on how new/used you want to go. Anything else I can add to this as the day goes on, I'll add to it. Monitors are a dime a dozen, get one thats easy on the eyes, but shop around. Every ones opinions on monitors will be different. I would suggest no smaller than 17" though.
*sorry if grammar sucks, at work atm, and was in a hurry lol*