The actual compiler that ActiveState uses to build their 64-bit perls is the Microsoft Platform SDK for Windows Server 2003 R2 and it's still freely available.

Not sure if that's the best link to getting it, and be careful that the download links don't in fact point to the updated (2008 ?) edition instead, though it's not the end of the world if you end up with the updated version.
That's the only MS Compiler I use with 64-bit ActivePerl, though I think there *are* 64-bit versions of Visual Studio freely available.

(I generally use mingw64 with 64-bit ActivePerl ... to each his own ;-)

Cheers,
Rob

Update: Not so sure now that it *is* still freely available. On that webpage I see "This SDK is available as a low-cost CD". I think that wasn't there before - instead there was a "Continue" button that allowed one to proceed with the 2003 download.