OK Steve, I had a few minutes at lunch so threw up a spec system for you. I am going for the following:
Case
PSU
HDD
Optical
Card Reader
Vid card
OS
I will then do a CPU/Mobo/RAM combo to go either Intel or AMD, depending on how high end you want to roll.
Decent case for $50
http://www.newegg.com/Product/Product.aspx...N82E16811147153
550 W OCZ PSU for $45 after MIR
http://www.newegg.com/Product/Product.aspx...N82E16817341022
WD 500 GB SATA HDD for $56
http://www.newegg.com/Product/Product.aspx...N82E16822136073
Lightscribe DVD writer for $32
http://www.newegg.com/Product/Product.aspx...N82E16827106335
Card reader for $10 because you just need them nowadays
http://www.newegg.com/Product/Product.aspx...N82E16820609298
OS You can buy a Windows 7 Professional key on eBay for about $10 right now, so $10 there
Video card is a little more important. I am sitting at $203 right now, so if I am aiming for $800, have about $600 for RAM, a video card, motherboard and CPU. Nice.
For a decent video card for $160, the ATI 5770 is hard to beat at that price.
http://www.newegg.com/Product/Product.aspx...N82E16814102864
If you wanted to go bigger, the 5850 is around $300 and a monster
Let's say the $160 card, though. We are sitting at $363. At this point, I am going Intel for high performance and a Crossfire board to boot.
CPU is the Intel Core i-5-660 for $208.
http://www.newegg.com/Product/Product.aspx...N82E16819115219
Now we are at $571 with a very nice build. Mobo and RAM is all that is left:
For the mobo, this is mine and I love it - $115 and Crossfire ready:
http://www.newegg.com/Product/Product.aspx...N82E16813157171
So now we are at $686 and just need RAM. 4 GB is all we need.
http://www.newegg.com/Product/Product.aspx...N82E16820227495
That is my RAM for 4 GB at $80.
Grand total is $766 plus a few dollars here and there for shipping.