What kind of snags did you run into? I am thinking of upgrading mine.
Well, initially, I tried to install Panter onto the same partition that Jaguar was on, using the "Erase and install" feature. Unfortunately, doing this also erases the various drivers and settings that XPostFacto had just installed prior to launching the Panther installer. The result for me was that the Panther installer reached the first restart (before prompting for Disk 2) and simply hung. I was able to boot into OS 9 to restart XPostFacto and reinstall all of the extra drivers and settings, but when I tried to continue, Panther wanted to basically begin the installation process all over again. My solution was to completely erase and format the partition where I was installing Panther, and then to begin the installation process again using XPostFacto from OS 9. After doing this, everything went very smoothly.
I just realized that my post might not be too clear if someone didn't know how XPostFacto works. Basically, you download XPF onto your drive (you obviously don't want to put it on a partition that you'll be erasing and formating - I put mine on my OS 9 partition). Then, you insert the Panther CD and launch XPF. From XPF, you select the partition where you want to install Panther (you can also change various options which I didn't touch) and then click "Install". XPF copies all of the necessary drivers and settings to your machine and then restarts the computer. You'll then see the normal Panther installer, and everything after this should proceed just like any other Panther installation.