Dual or single?
The 2004 single 1.8 and dual 1.8 can take up to 4gb PC3200 DDR RAM. You can pick up an extra 2gb's for around £30 over here in the UK. 80gb Hard drive is very very tight for a pretty damn powerful G5, they take your standard 3.5" SATA drives, there's two drive slots so I'd look around for maybe some WD blue drives. Or you can look at refurbs or used drives on eBay (cheap as chips). As to a graphics card, you may want to upgrade that too, but 64mb is okay for all non gaming stuff. If you would want to upgrade your graphics I'd look a tmaybe a 9600 XT. They're at 128mb VRAM or maybe if you want to play some games look at an Nvidia Quadro FX 4500. They're nice cards and have 512mb VRAM.