"Windows Media Technologies Is Incompatible..." Information.
It's getting narrowed down! Currently it appears that wmploc.dll in C:\Windows\System32 is the file causing hell for some users while trying to WMP 10. The solution might be rather simple, navigate to C:\Windows\ServicePackFiles\i386 and copy wmploc.dll to C:\Windows\System32. Now, run the WMP 10 installer again and see what you get.