Okay, going to upgrade my perfectly stable system to Leopard. Wipe and clean install or upgrade? I'd rather not go through re-installing all my apps (and keychains and all that crap), but I will if it's absolutely necessary.
I initially did an Upgrade, but didn't really like how it kept all my login items, etc. Course I was one of those people that used to reformat a decent amount back in the early XP and Windows 2000 days, so I can go from a clean wipe to fully customized system pretty quickly.
That being said, if you want to keep everything how it is, just upgrade. Worst case if you're not happy with that, you can wipe and install. Backup before you do anything just in case.
Also, make sure you install the latest version of APE if you are using it, as I believe older version cause that blue screen error. Or remove it entirely, I forget what the protocol is for it.