Without knowing how much RAM/HD, etc. it has, it's tough to be certain. One of my Macs is a 500 MHz G4 laptop with 512 megs of ram and in the past six months I've used it for various roles, including:
-installing OS 10.4 tiger server and running it as a file server on my home network
-carrying it around as a roving laptop to stay in touch with email and such while traveling
-using it as a Retrospect backup server to back up all the Macs on my home network
-using it to host my iPhoto and iTunes libraries to share with all the computers in the house
There's plenty of life still left in a G4, especially if it has even a minimal amount of RAM.