Hi Goose. You will have M$ Paint. While this is not really suitable for the serious repainter I have seen some remarkable results from people using it. This would be fine to practice the basic principles. Not everyone (including me) has the talent to be a repainter. Download the latest DXTBmp here.
http://www.mnwright.btinternet.co.uk/index.htmYou will need it to convert the textures before & after editing. It should already be set up by default to work with MS Paint. DXTBmp Help includes basic instructions & notes on the various FS texture formats.
From the available freeware graphics editors, I can recommend PhotoPlus 5.5.
http://www.freeserifsoftware.com/serif/ph/ph5/index.aspThis has all the advanced features you need & the interface is very similar to PSP. Like all free graphics editors I've tried it does have a few little peculiarities of its own. These can be easily overcome, especially if you have no previous experience with the more familiar commercial applications.
The alternative is Pixia, posted in the SimV Designs sections. This also has advanced features like Layers. From what I've seen of it, Pixia is more like PhotoShop.