Quote from mikkeri know hl2 doesn't have .wad files, but its proberly something quite like it. ".h2t", for examble, i don't know what its called. But i guess its not that diffrent. It needs bumpmapping and such, but if its possible to convert textures easily, it shouldn't be THAT much diffrent.
I thought HL2 used .tga files, all of which are found in a texture folder (ie. not an archive file, like a .wad)