First thing I did with my Blue/White PowerMac G3 was upgrade the processor from 300mhz to 1.1ghz ala a $100 CPU replacement from otherworldcomputing.com
It's now got 1gb of RAM, an 80GB HD and runs Tiger 10.4.11 quite fine. Use it as a music server only right now, but it'll still keep up for a while - browsing, e-mail, iWork, anything I've thrown at it, been fine.
