I've fixed my WinMPQ download, so it should work now. These changes are in the new version:
-Fixed a bug which caused WinMPQ to reload the archive when adding files. -The mpq archive listing will now be reloaded if a script is run which modifies the currently open archive. -Added Warcraft III maps (.w3m files) to open dialog filter.
I was going to upload a new version of WinMPQ today, but WinMPQ.zip got corrupted on my disk, so the WinMPQ download won't work right now. I should have this fixed later today.