Beginner Hardware Questions, ~here they come again~ Options

[Branch1999]

I'm just getting started, using Logic Gold on OS9.2 to lay out some midi tracks that I want to layer over with sampling, acoustic and electric guitars, and vocals.

~mucking about~

I'm using VST instruments and effects, laying notes down by hand, haven't saved up for a keyboard or sound card yet.
Around this point if I add any more effects or instruments I tend to get a message during playback that says something along the lines of "Mac AV overload- Not able to process sound in time"
Is this due to my soundcard? I've assigned more ram and it had no impact. (G3 450Mhz 500meg RAM) I know my system is getting a bit on the obsolete side, I've been spending too much time staring at the 1 gig dual processors... Should I consider a new system at this point or will my machine make it another year or two? Should I hold off on buying a new system in hopes that with the Emagic buyout the new Macs will come out with stronger soundcards in them?
Just looking for general direction before I go out and start dropping money (it's way too easy to do, even when you shouldn't be spending it)
Any help is much appriciated. Thanks!

[Branch1999]

I've started playing with that- thanks for the great ideas, Synthetic & bjkiwi. I made audio track versions of anything that depended heavily on effects, and just turned the effects off on the rest of the tracks till I'm ready for a mixdown, that seems to have made a big difference. If you come across anything about that PCI card, please pass it on, I'm trying to get whatever milage i can out of my system.
Thanks for your translation offers Presto, I haven't spoken French since high school and hardly remember a word.

so.. umm.. data5, don't suppose you have a soundcard I could borrow...?

Thanks for the help everyone, now if I can stop playing warcraft 3 for a couple days, I might yet be famous.
...if only Blizzard would stop putting out new video games every time I start to get productive...