Well... Heres a good basic example of the system layout i would reccomend
CPU Athlon 1.3 GHZ
Video Card : Geforce 2, Geforce 3, Geforce 4
Motherboard : One that is Athlon compliant preferably one that supports DDR ram.
Sound Card : Sound Blaster Audigy
256 Megs of DDR RAM
400 WATT power supply
And of course and ATX tower to house your computers hardware in.
That should be able to handle just about anything you would want to do in terms of multimedia.
You might also want to get a decent DVD drive for it and a decent burner.