I installed everything works just fine, when I open Xtra editor special, base, alternative, doesn't matter, it doesn't open but an error box pops up that says C:/Games/Starcraft/SC Xtra Editor Special.exe is not a valid Win32 application.
Makes no sense.

X-tra Editor won't run on Vista and I guess it won't run on WIndows7 neither.

As far as I know, General Mengsk didn't fix this windows compatibility problem.

I recommend using scmdraft2.

fartyedit is better than Xtra if you'd rather use a staredit mod.

heres a quick link to scmdraft
http://games.softpedia.com/get/Tools/Starcraft-SCMDraft.shtml

or if you have winrar you can get the latest one
http://www.stormcoast-fortress.net/temp/Scmdraft2-setup.rar

But if you want to keep using xtra editor, try and redownload and reinstall if you haven't already