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!