There is also using Alpha Channels, which was explained much better than I could hope of explaining it, by Vurt, in one of my threads.
Here's the link (
http://www.lucasforums.com/showthread.php?t=206262&highlight=making+shiny+textures)
And here's the post.
Create a file with the same name as the texture, except for the extension which should be .txi. The file only needs to contain this:
envmaptexture CM_BareMetal
Use notepad, and when you save make sure you have selected "all" for "save as type", otherwise it will be named yourtexturename.txi.txt - and that wont work.
In the alpha channel of the texture you then select which parts you want to be shiny. paint black=makes that part shiny, grey = a bit less shiny, white = no shine. An alpha channel that is completely black will make the whole armor shiny. To understand what alpha channel is (if you dont already) i suggest that you read up about it, there are many tutorials out there.
To add on a little bit, alpha channels in gimp can be found by first going to Colors, and then to Color to Alpha.
Hope this helped.