How can I check to see if my TGA will work in WoW?

I'm going to assume you have Photoshop. You should be able to follow similar steps for PaintShop Pro.

1. Open up your TGA. (Figure 1a, Figure 1b)
2. Look over at the layers palette (Figure 2).
3. Click on the Channels tab (Figure 3).
4. Check to make sure an alpha channel exists. If you are using the example image mentioned above, then it should. If it does not, then you will likely not see the results you are hoping to once you get the texture into WoW.