Dual 2.0 Rev B powermac crashes frequently with BOINC

I just got a Dual 2.0 REV B Powermac (10.3.4). Boinc seems to crash it after a few hours of running the service.
At first I installed the old version and I got the Mac screens of death (grey's desktop with a multilingual message telling me to restart with the power button).
Now my powermac locks during the screensaver at some point - fans at full blast but not much heat coming out the back - and I have to hold down the power button to restart.
The system is completely stable without BOINC running.
Any suggestions?
Thanks