I successfully built the debug configurations of ptlib 2.4.5 (static), h323plus 1.21.0 and simpleplus 1.21.0 in VS2008SP1 + WinSDK 7.1 on Win7/x64.
Audio and text work fine. However, video does not work: "No Video Grabber available Disabling Video Support!".
DirectShow support in vidinput_directx.cxx is compiled successfully and the DirectShow branches in simpleplus/main.cxx are active, since P_DIRECTSHOW is #define'd as 1 in ptbuildopts.h. I tried #define'ing P_DSHOW to 1 as well in simpleplus, without any difference.
As far as I can tell, the problem is that the DirectShow service is never registered on startup.
I expanded the PCREATE_VIDINPUT_PLUGIN(DirectShow) macro in vidinput_directx.cxx to put a breakpoint in PPlugin_PVideoInputDevice_DirectShow_Registration::<ctor>() and that code is compiled but never executed. Actually, it appears to never be mapped into memory at all, which should imply that the linker is removing it from the final EXE, but adding /OPT:NOREF in the build config of simpleplus does not make a difference.
However FakeVideo is registered and it also uses the PCREATE_VIDINPUT_PLUGIN() macro, and I can not spot any difference between the way FakeVideo and DirectShow are compiled and linked.
The only reference to a similar issue I could find is from over one year ago:
http://lists.packetizer.com/pipermail/h323plus/2009-August/001165.html
But the current code already uses PCREATE_VIDINPUT_PLUGIN() and, as I said, FakeVideo uses the same macro but is correctly registered.