try this:
first (as root) run: echo 1>/proc/sys/kernel/sysrq
then run tremulous as: tremulous > tremulous.log 2>&1
to catch the standard error as well as the standard output. when tremulous freezes, press alt+sysrq+s (sysrq is on the same key as printscreen) to sync to the harddrive (the kernel will buffer writes to the hard drive so it can write in larger chunks) and then alt+sysrq+k to kill all processes on that terminal (at which point you may need to manually restart X, but it sure beats a hard reboot). if none of the sysrq commands work after tremulous froze (try alt+sysrq+h in text mode to make sure they work before) then you should check your kernel logs to see if it is panicing. (and if this is too confusing, say so, i will try to explain things more)