How many processors do you have? If you use phpbb, then yes, you use MySQL. You can tune it so that if responds quicker. I would also suggest adding in a php caching engine to help serve pages faster.
thanks for the info^ i was thinking of installing APC (Alternative PHP Cache) do you recommend that? i have: CPU 330 @ 1.60GHz
Sounds like you only have one processor then...? If that's the case, then you load averages are way to high. 100% usage of the processor would be a value of 1.0. APC is good, I've had good luck with eAccelerator as well.
by the way wouldn't this cause my server to crash everyday (the APC)? as i have read somewhere that it causes crashes everyday
I have my doubts that this would cause a server to crash if it is configured properly, as I know many people use it. I would install it, and if you start having issues with it, then go to the next step.
mysql could be the culprit. may be too many long queries. just use the top command and check which process is taking too much cpu.