You used to get a free copy of photoshop LE with the purchase of a Wacom tablet or something similar.
I looked and that is still the case. So for $58 you can buy photoshop LE brand new and get a free wacom! π
Check amazon.com
It's ususally cheaper than buying photoshop LE alone. (by about $20)
Here is a link describing the difference between the photoshop and photoshop elements (or photoshop LE).
http://www.differencebetween.net/object/difference-between-photoshop-and-photoshop-elements/
If you get too advanced for photoshop elements then you shouldn't have a problem using GIMP at that point.
here is a link to the tablet
http://www.amazon.com/Wacom-CTL460-Bamboo-Pen-Tablet/dp/B002OOWC3I/ref=sr_1_1?ie=UTF8&qid=1297818588&sr=8-1