Like suike said, try the open-source GIMP from www.gimp.org. It is as good as photoshop and its filtering options are far more superior. Just give yourself a week to get used to it.

I am more or less accustumed to Photoshop but I do think that the Gimp can do most the job as good as Photoshop. Itis free but what a pity that there are not many tutorial available for advance process like in Photoshop

I think you can get Gimpshop.. It is sort of a skin on Gimp which makes it easier to use for Photoshop users..