That's not really my area of expertise. The images themselves aren't too hard to make but I believe that you then also need to create xxx _neg files as well, and I don't know how to do that. I guess if you wanted to get started you could download VTFedit or get a .vtf plugin for GIMP or Paint.NET or whatever image editor you use. Essentially, make the images that you want (with a transparent background) in a 256x256 square and save it as a VTF. To see what the filenames should be, either check manually through GCFScape or look around this site and see how other HUD-makers do it. That's all that I can really say right now, sorry.