If you don't want to buy photoshop you could always give the gimp a try. It has many great functions. The only problem with the program is that the user interface is not very good, but I quickly learnt a good way of using the program. When I open an image I press F11 to get a full screen view of the image. I then access all of the tools by right clicking on the picture which presents me with a menu with access to all the tools.
It would be much better if the interface looked more like photoshop, and it would be much more efficient, but you quickly learn to live with it. There are even books on using GIMP now. One was published just recently.
The reason I use GIMP is because it's the only decent photo editing program for Linux. I have windows, but I don't want to reboot my computer every time I want to edit a photograph, so I learnt to use GIMP.
Incidently, if anyone else here is using Linux, there is an excellent photo manager called F-Spot which I've now started using.
