What I mean is, if you can select only Windows to be your default OS when MAC boots? I would like my IMac to boot in win xp by default and the option of OSX boot being hidden. Is that possible? I need that for a software inspection in case they come to check software licenses on my computer. So when he logs in, Imac boots by default in Windows, not showing that it can boot in OSX also, so the inspector thinks no other OS is available? THX a LOT!

Hold down the option key when the Mac boots up. Select what you would like to boot, OS X or XP. Boom.

You can select whatever partition to boot from in Startup Disk in System Preferences. You cannot "hide" the OSX partition if you select Option key as pointed out in the above post. More importantly - what do you have to hide???