Hi,
Welcome to the HWT Forums.
Skins@HWT should have everything you need to get skinning. The
tutorials section contains tutorials from myself, Sandwichwarrior and Ricocet on general skinning, a tutorial on making TGAs and WTPs from RSH files by Danimator and a couple of tutorials on making areas team colourable/non-teamcolourable by me (again).
As for tools, I'd recommend the
Dawn of War Texture Tool. It'll extract WTP, RSH and RTX textures to TGAs/DDS images. To edit TGAs you'll need something like Photoshop, Paint Shop Pro,
The GIMP, or any other program that can save TGA images (possibly things like Corel Paint or whatever it's called). DDS images can be edited with Photoshop (with a plugin) and The GIMP - I'm not sure about other apps.
If you've got any more DoW skinning questions, stick them in the
Skinning Questions thread
Hope you enjoy your stay and find some useful tools/tutorials.