I'm working on a flag skin which has transparancy (with envmap)and text on it, but when I test it in game I can't see the transparancy/envmap, and the texture is "reversed" so from one side I can read it normally but at the other side it's "mirrored".

Can these things be solved?

use $vertexalpha or other such variables in your VMT file. As far as the reverse texture, you can't do anything except create your own flag model and make the texture non-reversed on both sides.

EDIT: i just wrote a bunch of crap that didn't answer your question, sorry :S.

But Dash is right, with textures on brush they are simply mirrored on both sides of the face. So you'd have to make a model where you can apply specific textures to both sides of the face, being the flag part.

I think the way the default dod source flags get away with it is just that the icon on the flag are symmetrical and so when they're mirrored they just look the same both sides.