To make you woes less difficult i suggest going to download.com and getting "mac tracker" this handy app will tell you all the info about macs ever. How much you can expand memory what can be upgraded ect. Cool thing is that mac tracker is free, comes with info about every mac ever and is extremly help full.

For a p2p app that wont bogg your comp try out poisened. Got to mac-p2p.com, it connects you to alot of diffrent peer 2 peer netwoks even kazaa and gnutella. Furthermore it only uses 10% of my comp speed instead of the horrible 80% of lime wire. I tried pro and its still the same slow thing. So try out man.