SharedMedia howto for adding a new media class (in this case, the "glow" class, for the Aloft addon):

1. Before taking any other action, edit "MyMedia.bat.txt", distributed with shared media; two changes must be made, affecting a range of lines.
   
   At or around line 12, add the line:
   

   mkdir ..\SharedMedia_MyMedia\glow

   At or around line 70, add the lines:
   

   echo GLOW
   echo.>> ..\SharedMedia_MyMedia\MyMedia.lua
   echo -- ----->> ..\SharedMedia_MyMedia\MyMedia.lua
   echo -- GLOW>> ..\SharedMedia_MyMedia\MyMedia.lua
   echo -- ----->> ..\SharedMedia_MyMedia\MyMedia.lua
   for %%F in (..\SharedMedia_MyMedia\glow\*.*) do (
   echo %%~nF
   echo LSM:Register("glow", "%%~nF", [[Interface\Addons\SharedMedia_MyMedia\glow\%%~nxF]]^) >> ..\SharedMedia_MyMedia\MyMedia.lua
   )

2. Follow the instructions in "INSTRUCTIONS for MyMedia.txt" (distributed with SharedMedia) to create the "SharedMedia_MyMedia" folder.
   
3. Add your glow texture file(s) to "SharedMedia_MyMedia/glow" (examples of valid glow texture files can be found in .../Interface/AddOns/Aloft/Textures).
   
4. Follow the instructions in "INSTRUCTIONS for MyMedia.txt" to create "MyMedia.lua"

Alternatively, you can leave MyMedia.bat.txt alone, and stitch your stuff into "SharedMedia_MyMedia/glow" and "MyMedia.lua" manually, yourself (once they are created, per the instructions in "INSTRUCTIONS for MyMedia.txt"). This will require you to add lines (one per texture file), in MyMedia.lua, of the form:
Disclaimer: Your texture files must be valid/correct Blizzard texture files. getting these "right" can be a bit tricky. Some documentation (which at least discusses this issue, at least vaguely) is available here. Note especially the "power of two" aspect ratio issue (Aloft glow textures are for the most part 32x512 pixels in dimension). The TGA alpha channel must also be used to leave areas in the texture image clear. Finally, all of Aloft's glow textures were created using GIMP.

Disclaimer: You must exit and restart the game completely in order for new folders/files in .../Interface/AddOns to be detected correctly. So, make sure you restart the game after creating the "SharedMedia_MyMedia folder for the first time, and/or after adding any file to the subdirectories there. (In contrast, you should be able to edit MyMedia.lua textually, and bring in changes just by reloading your UI; as long as there are no new files...)

This has been tested using SharedMedia 3.0.3-178.