thank you to both of you for these quick answers !

I'll check the mentionned articles.
More questions:

So… would you advise to do a back up of the system
before I move pictures, music etc to a partition on the external drive or
after ?
What about a sandbox ? in that case wouldn't it be the reverse (creating one
after I removed them) since the users files are shared with the HD and all those pictures, music etc would then be erased ? (did I understand how a sandbox works? )
I have made 4 partitions on my FW external drive. When I'm sure that Tiger works fine, and I have a bootable back up of it, I'll be able to free the Panther partition (100GB). For the moment, I still have 2 partitions of about 50GB and 1 partition of 100GB.
thanks again
atipani