Okay the system you are describing can be made by the lowest end parts available;
-Athlon 2000+
-ASUS A7N8X-X
-512 Mb DDR PC-'whatever's the cheapest'
-80Gig Western Digital HD 8Mb Cache 7200 RPM
-Radeon 9600
-Case (make sure has 350W PSU and is ATX)
-keyboard & mouse
-DVD drive, cd-burner, DVD-burner, whatever the hell you want
-Monitor
There. An insanely cheap computer that will do what you claim you want it to do. Definately not great by todays standards. Can get a higher Athlon chip ie 2800+. can also get a diff graphics card if you want to.