Compiling extensions in VC++6

I was wondering if anyone here had any experience with building any of the extensions supplied with the PHP source code? I have so far managed to successfully compile both the CGI and Apache module versions of PHP itself, but I am having mixed luck with the extensions. Some I can get libraries for and they build fine, but GD comes up with so many errors, none of which seem down to a missing library - any help greatly appreciated... Mikey