If you are going to jump to the new intel Mac, be ready to wait for native Adobe products. Final cut uses the universal binary but the current versions of photoshop, illustrator, macromedia studio etc... only work on intel macs with rosetta.
The G5 towers seem to be the best bang for the buck right now. If you can get a used dual processor, I'd snap it up and fill it with ram. When your rendering video the more ram the better.