cannot format drive in use

I have two hard drives. On one I have Vista and XP installed, and on the other I have OSX installed. I’ve been trying to install openSuse 11.0 along side the OSX installation, but every time I go to format the drive using either openSuse installation or gparted it gives me an error saying “the drive is in use by the system”. I even tried erasing the OSX hfs+ partition and starting with a completely unpartitioned drive. It still says the same thing when I go to format the drive with any filesystem. What am I doing wrong? The strange thing is I can format the drive in Vista (and I assume XP) but it will only let me format it to ntfs which is pretty much useless in my case. Why won’t linux do it?

The OS you’re booting to apparently has written files into the OSX partition.

Resolve by booting to a LiveCD instead,
GParted – LiveCD

If I were to guess, the bootloader you’re currently using lives in that partition.