Hi Rattler,
I use PhotoShop version 7.
It's really quite a versatile program with a steep learning curve. I've been using it for a few years now and still find new and interesting things about it that I had no idea existed.
As for GIMP, I've never used it, but as I understand it, a lot of skinnners do. And you can't beat the price
A quick look over at the 'zoo produced this link:
http://forums.ubi.com/eve/forums/a/tpc/ ... 3071064713
EDIT: The links in that thread have been moved here:
http://www.flightsimguides.com/
Skinners Paintshop is down at the moment, but check it out when it's back up. A wealth of knowledge and a number of good basic tutorials to be found.
My best advice is to just do it. Pop a skin or a void into GIMP (or whatever program you finally decide on) and have at it. Explore the various tools and become familiar with how it works. Once you get a feel for it, start asking questions in one of the above forums. With few exceptions, Ive found the skinning community to be very patient, helpful and friendly. If you do end up with PhotoShop, I'll be more than happy to answer any questions or supply you with templates.
I look forward to seeing your first skin,