Hello, 
I'm running MOTU Digital Performer 4.12 on a 1.25 Ghz G4 with Panther and 1.25 GB of RAM.... I would assume that with these respectable specs I could play more than one or two tracks without a pesky error message telling me that I've overloaded the system's capabilities.  But alas, no.  I've played with the buffer sizes and I'm still having problems.  
I am actually recording to the system hard drive and not to an external, perhaps this is the problem?  Anyone have any suggestions?  
oh yeah I'm using an M-Adio Firewire 410 
thanks in advance for any assistance
-throcke