Be sure to have a full backup of your current boot drive before upgrading to Snow Leopard. I don't know if Photoshop CS2 works or not (I've read the compatibility reports :-{ ). You'll probably need to install Rosetta (not a standard install) and test for yourself. I'm running CS3 and it looks like everything is fine.
A late thank you, and a follow-up: Bought the SnowLeopard update (it´s surprisingly cheap for an apple product... ) and made a test installation on another drive (after taking the Leopard drive out). Rosetta installed as well. Here are my findings (with reservations that there might be bugs or gotchas that I haven´t found yet):
Lightroom 2.5 runs perfectly, accessing my present library on its own drive.
Photoshop CS2 runs fine, and cooperates with Lightroom without a hitch.
Light Zone (latest version) runs fine, too.
Capture One (again, latest version) seems to run OK as well, but haven´t had time to test it much.
My Epson 3800 needed a driver download directly from Epson (wasn´t in Apple´s library), but seems to work OK.
Several non-photo related programs had problems, though, so I´ll postpone my upgrading. At least it seems I won´t have problems with any of my image processing software...