http://bugs.winehq.org/show_bug.cgi?id=21097
--- Comment #18 from Eduardo I. perseguidor@gmail.com 2011-03-18 08:23:38 CDT --- So summing up it seems one would had to either compile or get libtxc_dxtn.so so as to enable S3TC support on recent Mesa.
Note for other Debian users: it's on debian-multimedia, but installing it doesn't seem to make any difference. I guess it may be because I'm running a 64 bit system and it's a 64 bit library when I probably need a 32 bit one for MISE, but that's just a guess.