Yes you can.
You don't need to format. Lookup a command called "convert".
I posted this while back... Go to here @ Microsoft's Support Site . Quite simple really... but the chances are, you will get the "error" message saying "Convert cannot gain exclusive access to the drive letter drive, so it cannot convert it now. Would you like to schedule it to be converted the next time the system restarts? "
What proxops-pete said. Just remember that you can not go back once you make the conversion. (Patition magic might allow you to go back to fat not sure, plus it costs money)