If it's any use to you, Inline::CPP builds and tests fine with ActivePerl-5.10 and the MinGW compiler (which you can install by running ppm install MinGW). If you do try to build with MinGW, make sure you start with a fresh source installation - running 'nmake realclean' first is not enough.
I use Parse-RecDescent-1.94 as there are problems with later versions of P::RD and Inline::CPP.

Inline::CPP also builds and tests fine using Visual C++ 7.0 (on a perl-5.10.1 built using the same compiler), so I guess the problem must be specific to Visual C++ 6 - which I don't have.

Cheers,
Rob