Continuously funning fan


I am using an iBook G3 10.2.8 (yes, it needs updating).
When I use it for sometime (30 plus minutes) on my glass top dining room table, the fan starts and continuously runs until I put the Mac to sleep.
Am I damaging the iBook? It doesnt' feel like it is getting to hot.
Any suggestions?
Reset the RAM?
You could try a temperature monitor program like this:

and (if your laptop has a sensor for it) see what temp. the fan is coming on at and you might be able to find out what's causing it to stay on. Post back on the results.

Just a second thought; are the air intake vents clogged with dust?