Archive and Install will keep your old operating system in a folder (I forget exactly what it's called) and will preserve all of your network settings (as mentioned) without requiring a partition. If you've got recorded this info and backed up your important data, a clean install might be your best bet. I'd probably opt for a clean install, which effectively wipes your hard drive clean and then lets you start fresh with a new operating system. You'll have to reenter all of your network settings, etc., but the likelihood of any issues is decreased. As mentioned, lots of people seem to have problems with archive and install.
(A good way to save your settings is to open the relevant network preference panes and use Grab to save pictures of your settings, this works well for email settings too).
There's one downside to this approach, though. All of the software that shipped with your computer that isn't part of the OS itself, (things like OmniGraffle, etc.) will not be available if you choose this option. (You still get itunes, mail, all the standard stuff). If that doesn't bother you (I know that I rarely use that stuff) then this is your best bet.
Panther is much snappier than Jaguar, so you'll probably be glad you made the switch.
