In your case, this is a tough one. First off, if you buy the MacPro you’ll have to upgrad Final Cut Pro if you haven’t done so recently. It’s very cheap, but check the list first to be sure that this price won’t surprise you later:
https://www.apple.com/universal/crossgrade/
If you have the whole studio with Final Cut Pro 5 it’s only $50. If you have some other version of Final Cut it’s more, but not too much. Shake will also require a $50 upgrade. Anway, you’ll HAVE to do that to use them on the MacPro because it uses Intel chips. The G5 will run the Apple software you have now without upgrading.
Secondly, ALL of your Adobe software is not optomized for the Intel chips yet. It won’t be until next year and you’ll have to buy the next version number upgrade to get it. What does this mean? Well, unlike Final Cut it WILL run on the MacPro…you don’t HAVE to upgrade it, ever, if you don’t want to. It will be running through an emulation enviroment on the MacPro, though. You will never see that program, you don’t have to do anything. It “just works” without you having to do a thing. It does make it a little slower, though. So what will happen is that After Effects will run just fine now, but when you upgrade to the new After Effects next year it will suddenly become much, much faster.
So there’s the catch, if you buy a MacPro much of your software will be much faster than if you buy the G5 but SOME of it will be slightly slower. But if you upgrade all the software next year then ALL of your software will be faster than if you’d bought the G5. If you buy the G5 you’ll be better off THIS year, but by next year you’ll be using a slower computer than you could have had if you’d just put up with slightly slower Adobe software for a little while.
So really, it’s more of a personal choice. We can’t tell you what’s “best” here because it depends on what matters to you most. If you use After Effects 90% of the time then I’d say get the G5. If you use Final Cut Pro and Shake 90% of the time I’d say get the MacPro.
There’s one more thing to remember…I’m going on and on about Adobe prodcuts being “slower.” What do I mean by that? Generally they’re about 15-25% slower than they would be if they were upgraded next year. Ok, but remember, you’re using a Powerbook. You didn’t say what Powerbook it is, but the MacPro will be at least, AT LEAST 500% faster than that machine. You said you’d had it for a while so I’m betting the difference is even MORE than that.
To me, that’s what makes the difference. Yes, After Effects will be slightly slower on the MacPro than the G5. But you know what? It’ll still be way, way, WAY faster than what you’re used to now. So if it were me, I’d get the MacPro and be happy that my Adobe products are going to get even better next year. But that’s me. If you think the G5 will serve you better, then go with that.
And as I tell all Mac Tower buyers, buy at LEAST 2 GB of RAM…4 would be better. Don’t buy it from Apple, go to crucial.com to get it, and please follow the Mac’s instruction book (available on Apple.com if you lose it) because which slots you put the RAM in does matter.