Logic board problem?

Just recently I got two You Have to Restart Your Machine errors in the same day. Once I was JUST logging on, the other was when I was surfing and converting some songs. Is this a normal occurance I should be aware of, or should I sent it in while it's still under warranty (but then how they DUPLICATE the error!)? Thank you.

iBook G4 800Mhz, 10.3.3, updated to latest releases of iLife stuff except iMovie which is uninstalled (if that matters).