This has already been done for you, but if you're trying to do it yourself:

Download gnutls Win32 binaries, then open an MSVC command prompt and run:
lib /def:libgnutls-26.def (in the bin folder of the gnu32 download)

gloox: 
remove TLS server cpp and h from the VS project
define HAVE_GNUTLS in the preprocessor bit
add "#define ssize_t signed long" to the top of tlsgnutlsbase.h as a nice and nasty hack

