I've been just starting to use XS, and MS Visual c++ has worked great. I haven't done any XS work on *nix, but I used the standared perl docs and didn't have any problems. I have used NT and 2000 (I've heard that running 'perl Makefile.PL' on Win 9X/ME doesn't format the make file correctly for nmake, so you'll need to format it by hand).