Free Photoshop-like program?

[Quixote]

Hey guys, I'm currently looking to make a few images transparent for a webpage.

I have experience only with MS paint to get the job done for everything, but I'm needing now to make white parts on images transparent.
Is there a trial of Photoshop, or another free program to get the job done?

Thanks

 

[Splintert]

GIMP

 

[unicorn]

Before I got photoshop I used to use Paint.net

 

[Phonemelter]

GIMP

Such a wonderful program; I highly recommend it.

 

[Fierce Headmaster]

I vouch for GIMP.

 

[BattleOfValmy]

Definitely GIMP. I get Photoshop from my school for free, and while it is much better, if you don't have it and can't afford it, definitely GIMP.