From what i know, the discussion rules prohibit talk of intel powermacs, so..yeah.
To answer your question, buy the G5.
Why?
The imac has limited physical space for RAM, HD, and other upgrades. The G5 has plenty of room. the G5 may not be as fast as the intel macs but you will probably enjoy editing videos on it more. When you have to render a 2 hr project, the G5 helps alot.
Both intel Imac and G5 are fast, but the intel macs are generally faster at applications written for the intel processor (universal? i may be wrong).
I play Call of Duty 2 on my mac with everything at max, and it cuts right through it. i wouldn't know about the intel mac performance though.
anyways, buy the G5, you will most likely be much happier.