So your installation of Mac OS X 10.5 Leopard seemed to go perfectly until it came to firing up Adobe Photoshop, right? That was certainly my experience. Then came the dreaded "An unexpected and unrecoverable problem has occurred" message as soon as you launched Photoshop...
Well, it's bad news I'm afraid. According to this document on the Adobe web site, if you have Photoshop 7, Photoshop CS or even Photoshop CS2, you are "likely to encounter issues for which there is no resolution". There's a big tick in the NOT DESIGNED FOR OS X LEOPARD column, and that's it. Hard luck.
I trawled around the message boards, but nobody seems to have a workaround. It seems that you've no option but to upgrade - irritating if you were happy with your older version, but that, I'm afraid, is life. There's little to choose in price between the various software retailers, so it was off to good old Amazon UK (see left) for me. If you really need a working Photoshop right now, Adobe has a downloadable version in their web store, although it's over 750MB.