So over the past couple of months, I’ve been scrunging to sell my older parts in the effort to upgrade my desktop PC, which is mainly used for gaming and video capturing (miniDV camcorder). I don’t mind used parts so I found great deals and hitched up! 
Here’s the rundown…
Before:
CPU: AMD Athlon64 Socket 754 3000+ (OC’ed to 2.4 GHz)
Memory: 2x 512 MB Patriot PDP+XBLK memory
Video: BFG 6800GT 256 MB AGP
Motherboard: Chaintech VNF3-250
HDD: 100 GB IDE Seagate / 160 GB IDE Western Digital
Now:
CPU: AMD Athlon64 X2 Socket 939 4200+ (OC’ed to 2.5 GHz)
Memory: 2x 1 GB Patriot EP PC3200
Video: Sapphire X1900XT 512 MB PCI-E
Motherboard: Epox 9NPA+ Ultra
HDD: 250 GB SATA Hitachi / 200 GB SATA Maxtor
All I can say is… 
Dual core helps a LOT in multi-tasking… my http://folding.stanford.edu project is now crunching out faster than ever to find the cure for cancer! 
My games both look beatiful and runs so much faster… hee… the satisfaction of building/upgrading your own rig is just a pure sensation! 
Say what you will… at least I’m a very happy nerd/geek …