With the Sharp ROM, this disables the suspend and light dimming:
qcop QPE/System 'setScreenSaverIntervals(int,int,int)' 0 0 0
and this reenables everything again:
qcop QPE/System 'setScreenSaverIntervals(int,int,int)' -1 -1 -1
Sharp's version of Qtopia is slightly different from Trolltech's documented version. I don't think there is a way to disable only the suspend without disabling the auto-light dimming.