I've been trying to install the texture pack on the GOG installer but i keep on getting the "Run-time error ‘76’: Path not found" issue with the .ibt patcher. Now i tried the original installer i borrowed, it seems that i didn't get the error this time but installation progress seems to halt after .ibt patch progress bar.
Any solutions? should i patch to version 1.1? thanks!

Windows 8 needs a registry tweak, see http://www.gog.com/forum/thief_series/thief_3_john_p_textures

I also had to use the cleaner here to get rid of the half-complete install before I could try again.