Just got Jag?? With Panther around the corner?
Ok..first about partitions. I would only go with 2 maximum. 1 for OSX and one for OS9 if you wanted to keep it.
What I would do: wipe everything, partition the HD into 2, and install 9 on one and X on the other. Give your main OS the bigger side (or split it evenly into 2).
What I would do if I didn't need classic/OS9 (which I don't, so this is what I did): Wipe the HD, make 0 partitions, install OSX.
Backup: Since more than likely you are going to do a clean install, here is what I would do:
Emails: I have a hotmail/Yahoo account and send all my important email there...for safe-keeping until I can send them back. JUST IN CASE.
Music that I don't have CD's for: burn them to CD or put them on external HD. This is mainly for iTMS music I purchased.
Photographs: I burn them to CD or upload them to my server.
Misc. files that you want to keep: burn to CD or upload to .Mac or whereever you might have space.
I would only keep what is important...otherwise you can get the file again.
It's too bad you don't have iSync..cause then it saves a lot of time for Safari Bookmarks and such.
Also, another thing, what I do is go to each site that I have bookmarked and copy/paste the url (especially those that I don't recall easily enough) and send them to my hotmail account via email. Makes them clickable
Other than that..I say go for it and install.