Have not used partition magic since Norton's takeover of Powerquest so cannot comment directly, but used the original Partition magic for years with no problems.
Only advice I would give is to ensure that any vital personal data,(documents, Photos, etc.), on the drive is backed up before you start - Partition managers are safe but with any operation that moves data you have the chance, however small, of causing data loss.
Also as you are possibly moving at least one OS partition I would make sure you have the install DVD / CD for vista and Seven to hand just in case they get confused after being moved.
I'm sure everything will go fine just read through the help / Manual for Partition Magic before you start so that you know what to expect. It may be worth printing the relevant parts of the manual to refer to whilst working
Hope this helps