I’ve edited a 12hr video on a G4 imac with the 15″ screen and 768 megs of RAM.
That sucked. But it worked.
I now use a dual 2Ghz G5 and love it. The dual processors scream through tasks.
So to answer your question, stick a little more RAM in it, and you’ll have a good machine. But, IMHO if you can afford it, splurge and get the PowerMac, you won’t be disappointed.