There are many graphic design programs out there. I use Photoshop 5, some use Photoshop Elements (way cheaper if you have to buy), others use Photo Impact. Someone just suggested GIMP, which apparently is free on the internet; don't know the site, however.
I would suggest that you go to download.com or similar site and try several before you buy. You can also download some trial versions from the company websites. I know that the new extremely pricey Photoshop CS3 is on free trial, because I am using it! It is probably the most versitile and comprehensive program I have ever used. Try several programs before you make a decision. Different people like different programs.
Hope this helps.