I tried Elfie's skinning tutorial but I can't open rep_inf_ep3trooper.tga I get an error message that says
C:\BF2_ModTools\dta_***\Sides\rep\msh\rep_inf_ep3trooper.tga.option

What program are you using? GIMP? Photoshop? Paintshop pro? I use gimp and I never get any errors from it. You don't have to use file> open also. I never do. I just double click on the file and it opens with GIMP automatically. Try that. GIMP is not a program that causes problems, so you should use it if you haven't already.

H_BOMB wrote:C:\BF2_ModTools\dta_***\Sides\rep\msh\rep_inf_ep3trooper.tga.option

You shouldn't be trying to open the file that actually says .tga on the end. What I would do it go down to where it says (at the bottom of the "Open Image" menu, right above the open buttom) probably "All Files" or "All Images," click the arrow next to it, so a drop down menu opens, and scroll through that until you find "TarGA image (*.tga, *.vda, etc.)," click on it, and that will make it so you can only see the .tga files. Then look for re_inf_ep3trooper (with no .tga on the end).

EDIT: Oh, this is what to do with GIMP, but it shouldn't be too much different with any other program, just make sure you have it so you can only see TarGA images.