There are several Trial ware
programs you can use. Usually the trial period lasts 30 days. Trial ware allows access to high end programs for use on several projects without paying the price.
Adobe has Photoshop/CS and Coral has Paint Shop Pro.
Thing is the higher end graphics programs may require a 'late model' computer and lots of resources, and may require XP or Vista. The OS requirements probably aren't a problem, the hardware could be.
I would suggest Paint Shop
, last time I tried Photoshop/CS Adobe hadn't worked out all the bugs and CS was known to not install or run well (if at all).