In case you - like me - are unhappy about bootcamp 3.0, shipped with mac os x 10.6 "snow leopard", mounting your mac partitions read only in windows and assignig them drive letters, here's a heads up:

DO NOT TRY TO REMOVE THESE DRIVE LETTERS using the "Computer Management -> Disk Management -> Remove drive letter" way.

Windows re-sets the partition's type if you choose this option, and the EFI Bios of your mac will no longer regard the partitions as bootable. Even if you re-add drive letters, the partition type will still be MSDATA. Yes, windows really sucks big time.

having tried quite a few tricks, i have to say: it's not easy to get out of this trap. Simply changing back the partition type is not the way to go, as the GUID partition table is way more complex than i thought.

You will have to dump the partition contents using dd into partitions with a correct GPT, while being extremely careful about the /dev/disk assignments - these change from boot to boot! Another tip: The "dd" shipped on the OS X boot cd is horribly slow (and the dvd drive keeps spinning all the time), it ran at about 17MB/s for me. Take the time to install rEFIt using the rescue system, and boot an ubuntu livecd. The dd in ubuntu ran at 95MB/s. Saves you a few hours.

If you need assistance, please comment on this entry, i will try to help you - but be warned: this procedure requires console-fu.