How to best use two computers?

Computer #1= Pent III; 512MB mem; USB1 ports (slow); 2 HD's (40 GB each); CDROM drv.; and a RW-CDROM drv.

                            Dual boot: hd0 (primary)=Windows XP (I'll be dumping it once I save all wanted files).
                                                hd1 (master) = Ubuntu 11.10 oneiric ocelot

Computer#2= Pent IV; 768MB (plan to upgrade to 1 GB, max allowed); USB 2 ports; 1HD (40 GB); one RW-CDROM drv.

I am a musician. I don't use the pc's for game playing ( except chess). I've downloaded various multimedia/sound recording software and am learning how to use, and eventually choose my favorite programs. Then I'll set up a basic at-home studio.

I don't have a backup/storage setup and need to do that.

Internet setup: PC1 is cabled to my wireless router; PC2 using USB wireless adapter.

I am asking for any ideas on a basic plan (or detailed) I can follow to use my existing setup, until I later am able to spend more money to upgrade my situation.

Thank you, ~Leo