If you're talking about the stock Raven textures, just make sure Radiant is set for JK:JA, its in Edit>Preferences... You may have to restart Radiant for this to take effect. If you are talking about your own textures, you need to do the following:
1) Custom textures must be JPEG or TGA
2) Must be in base/textures/<mapname> where <mapname> is the name of your map
3) Both sides (dimensions) must be of a power of 2, this includes the following:
2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, etc. In game, 512x512 is pretty high detail, so only go upwards if really necessary.
4) Names of files must NOT contain spaces (the " " character), but may have underscores ( _ character).
Then do Flush and Reload shaders in Radiant and you should see <mapname> as one of the items on the menu. Click it and press T to see your list of files.