1. Get hold of photoshop (or Gimp, the free alternative) and optionally get the
DDS plugin(also free) for it, let's you open MB texture files.
2. Get
this PhotoShop file, I've included the UV map guide, shows you how stuff will be mapped onto the model. This one doesn't require the DDS plugin. Alternatively, in vc's textures folder find vc_body_male01.dds make a copy and start with that.
3. Open it up and on a new layer paint your designs. Either avoid painting over the seams (edges) entirely or make it so busy/complex that the discrepancies are hard to spot. But don't worry too much, just have fun.
4.
At this point you can just send it to me if you want to include it.
5. When you're finished flatten the images and make crop it to just the big left-hand square. Make sure the image is an equal height and width in pixels.
6. Save it as a .dds file, choose "DTX1" and "generate MIP maps" when the DDS window comes up.
7. Put it in the vc textures folder or whatever mod you're adding it to.
8. Go to
this section of the forum and get OpenBRF. That's what you use to combine your texture with a model. There should be plenty of info there on how to do the rest, good luck.