I realise it's a while since you posted this, but...
GIMP is a great photo editing program, it runs on Windows and Linux (and possible Mac). The latest version (I run 2.4.5 on my Linux PC) has most of the abilities of Photoshop, although the iWarp filter (in Distorts) is not as good as the liquefy function in Photoshop.
If you're coming to the GIMP from Photoshop, you'll have to get used to where things are (Layers, for instance, isn't in Image, it's in Tools.).
I don't have the plugin problem with Linux and the camara I have, so I can't advise on that issue.
There is a good book on the Gimp - "Beginning GIMP - From Novice to Professional" by Akkana Peck published by Apress.
If you're wondering whether or not to use the GIMP, download and run it. Its free after all.