I would assume it takes some getting used to the textures, but should be doable. It's just getting the measurements right.
Here have a look : This is the default tooltip
http://wowprogramming.com/BlizzArt/I...tip-Border.png it is replaceable, you just make a new PNG (or TGA, png might be easier though) and convert it to BLP. Load up the game (very important) and see what it looks like.