Hey, I don't know how late I am on this bandwagon, but I thought I'd jump on. I built a machine a few years ago (which still works beautifully) and I was wondering if you were looking for peripherals.
ASUS makes some great, cheap 1080p monitors for a little over a hundred dollars. I have one hooked up to my desktop PC and my PS3. They both display beautifully. Most of them come with a VGA, DVI and HDMI port. Some of them come with Audio options, so that's worth looking into. The Audio isn't great, but you can plug in a 2.1 speaker system into it into the headphone jack and cover that up.
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&N=-1&isNodeId=1&Description=Asus+1080p&x=0&y=0
If you check google shopping you can order a copy of Windows 7 Home Premium (you don't need anything more than that, to be honest) for less than 100 dollars
[link]http://www.google.com/products/catalog?q=Windows+7+home+premium&um=1&hl=en&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1280&bih=606&ie=UTF-8&tbm=shop&cid=4979755892271826252&sa=X&ei=t06XTraqOaTjiALB3aygDQ&ved=0CHQQ8wIwAQ#start=20[/link]
Mice don't HAVE to be expensive, but Razer mice (at least the ones that aren't made by Microsoft) are very reliable, precise and are well worth paying for if you want to shell out.
http://www.razerzone.com/
Also, if you can scrape up the cash and can find one, I still use my ancient gamepad/keyboard called the Ideazon Fang. The company's out of business, but Windows still recognizes it as a keyboard and it's the most comfortable setup for PC games I've ever used.
http://www.newegg.com/Product/Product.aspx?Item=N82E16823161023
Good luck, and happy gaming!