The art of compromise

P4 2GHz
MSI AWRDACPI non-SATA
GeForce4 MX 420
512 SDRAM (uncertain of RAM type; no idea how to even check)
15" LCD Polyview
ATAPI CD-RW 40x12
WD 80GB PATA

This system was bought four-and-a-half years ago, maybe five. I have about $1000 American to play with, but my hardware knowledge is rude. What should I add? Or upgrade? Or supplement? An actual audio card interests me (and decent speakers), but I'm thinking it'll take a new motherboard - I know little about either products.

Also, I'm barely a gamer these days, but I *am* after something that will at least handle Oblivion.

Fire away.

Okay, thanks. A good start. I'll have get some reading done on compatibility issues, but current priorities:

a. Motherboard (MSI again? I'm open, here)
b. CPU (Okay: 754- or 939-pin AMD 3000?  $85AU difference. Pins...?)
c. RAM (1GB DDR2)
d. Graphics card/sound card (EMU something--my music owns me; Radeon 9800 Pro)
e. Hard disk

Christ, this adds up...

Also: links, please. Not vendors. I'm after tech news sites.