Hi,
How I do it:
1. Make a copy of your plane's day texture and rename it by adding _alpha to the end of the filename (it should still end in .bmp or your favorite format). (I use the 24 bit version I save for backup when I need to re-edit the bitmap)
2. Load this new texture into your favorite paint program.
3. Now use the magic wand (or equivalent tool) to select all the lettering and other areas you do not want to have a reflective shine. Sometimes it's easier to select all the bare metal instead - whichever is easier.
4. Invert the selection if needed to get everything *but* the bare metal selected.
5. Fill the selected area with 255,255,255 pure white. This will keep the lettering, etc. from "fading out". Use a high "tolerance" setting to allow the fill tool to completely fill the area.
6. Invert the selection, choose a gray color around 175,175,175 to 225,225,225 or so, and fill the entire selected (bare metal) area with this color. The lower the number the greater the shine.
7. Save this bitmap file. Keep this file open in case you need to change the bare metal alpha channel gray color after testing in FS.
8. Open DXTBmp and load your day texture (I use a copy of the 24 bit version, pasted into the plane's texture folder).
9. Choose Alpha/Import Alpha Channel and say Yes/OK to the warning.
10. Browse to your new _alpha bitmap and load it. You should now see it displayed in the upper right corner.
11. Choose File/Save As and select Extended Bitmap from the choices.
12. From the drop down box select your desired format. For flyable planes I use 888 32 bit, for AI I use DXT3 (FS9) or DDS (FSX). If the plane has a _L night texture, use the same format as that one.
13. Save the file, overwriting the copied bitmap *in the plane's texture folder* (not your 24 bit backup!).
Adjust the value of the bare metal alpha channel until you get the amount of shine you want.
Hope this helps,