Here's a chart that shows relative performance of different Macs using a Logic stress
Not sure what software you are using, but I completed my
current album with a lesser machine.
I did have to freeze tracks, something
that is now not needed with my quad core Macbook Pro.
More RAM, and always keep
projects on an external hard drive.
With the OS and most audio apps being
64bit, you may want to upgrade to a newer Mac.
Studio G-fx 15inch quad-core i7 Macbook Pro Logic913