What you're describing is an open firmware screen, which you can get to by holding down "option+apple+o+f" at startup. If you don't hold this down and still get to this screen, there could be something wrong with your hardware- the RAM or L2 cache are usually to blame in this case. If it's just a one-time thing then I wouldn't worry. You could also try resetting the PRAM (option+apple+p+r at startup, hold down until you hear another chime). Also, when in open firmware, typing in "reset-all" and pressing enter will reset the PRAM for you. Like I said though, if you keep getting this, bring in your system because this is a pre-OS firmware related problem.