As Heero said, just reinstall Warcraft III from the original CD. (Be sure to back up any custom files/maps FIRST.)
And no, Warcraft III does not care where it's installed: my War 3 files have lived on D:\ since the Beyond The Dark Portal days.
[off topic] derich: Please introduce yourself to the Hive community in our [self="http://www.hiveworkshop.com/forums/forumdisplay.php?f=360"]Introductions[/self] forum.