Boggin' Down, my mac can't handle it Options

[aquaman]

I am using an eMac with a 700 MHz G4, 768 MBytes of ram, and have a music project in Cubase that has about 20 tracks. Every track has eq., and one or two plugin effects. This appears to be way too much for my Mac to handle because what is heard when it plays is just clicking....lots of clicking. I have to turn off most of the eq. and effects and mute most of the tracks to listen to anything. This means I can't mix this project properly. Does this sound reasonable? I suspect the bus speed is too slow because it happens every time I play the song back (i.e. not just the first time). I find it hard to believe that this relatively simple project is already sapping my mac. Certainly there are many people, on this web site alone, that are using comparable systems and doing more complicated things. Input would be greatly appreciated.
-Thanks