I hav'nt used PSP much, but I've never needed to leave Photoshop.  I'd like to say that Photoshop 9 is worth all that money, but would have to say that it has'nt changed all that much since version 7(Which first came with ImageReady(For .GIF work)  So, if you'rte looking to save a little $$, I would recommend looking for an older version of Photoshop, before PSP.

BTW - If you do'nt hink you'll need ImageReady You could pick up version 4 or 5(Whichever first introduced Actions...)