Try this free one, it has a lot of capabilities:
http://www.getpaint.net/index.html
It's not bad by all accounts, but there is no other photo editing program with all the capabilities of PhotoShop, it is the industry standard.
If you want PhotoShop, then your best bet is to see if you can find a cheap old version off the 'net, sometimes older versions are given away on magazine cover disks (but not that often because even versions back to PhotoShop 4 are still fairly capable). another option is to buy a discounted current version (which you can do if you are a student, or you know someone who is a student who can buy it for you and give 'em the cash).

Chock