http://www.gimp.org/ is free software with a lot of add-ons and a full programing language embedded as well as ties to various image manip libraries.
There are decent on-line documentation availabel and some (slghtly out of date) books written for beginners.
Finally this tools works "out of the box" with most cheap graphics tablet. My Medion 256grad A4 tablet requires drivers under windows but used Wacom drivers under linux or a Mac and works flawlessly - GIMP even detects if you are using the tablet mouse of pen!
I have yet to find a decent (free) flexible RAW converter for Fuji RAW formats - pity I cannot afford a high-end Canon :-)
Jacqui
p.s. I use a high-res scanner to import 35mm negs and then clean up/remove the graining - buying a high-res scanner (and extra mem for the computers) was one of my best image manip purchases!
My latest $work activilty is something called openCL - this is a programming interface for the compute engines within a graphics card.
This allows say a graphics program doing image manipulation to have access tothe hundreds or thousands of "processors" within the graphics card instead of just the one to six in your PC.
The nice things is that with a small overhead sofwtare such as the gimp can be written to use either or both sets of processors increasing photo manipulation performance.