yep you can get a 30 day demo of PS (CS4) - i wouldn't try downloading it on a dial-up connection...

as for the learning curve,  there is a LOT that you can do in photoshop, that said, you don't really need to learn EVERYTHING about the program, you just need to learn how to do the stuf YOU want to do...

What i use PS for when i'm dealing with photos in RAW format is totally different then when i'm using photoshop to comp a website, and still quite different when i'm working on a brochure...

i've been with photoshop since 2.5 (still have the floppies) and i'm STILL learning something all the time!

i can tell you, there are a few things that you were able to do "quite easily" in paint shop pro, that will be handled differently in PS and it will drive you crazy!! keep in mind you can still accomplish the same task but if both programs were identical in the process, one of them would be in a copyright violation :) 

if you have any problem we're always here to help.

:)
retrocity