Heroes 3 issues under XP or Vista.

Heroes of Might and Magic run on Vista, and almost any game or program runs on Vista. The most effective method, if it doesn't want to install, is to simply copy the already unpacked game to another drive. ;)
You can unpack (install) it, for example, at a friend's place. My game works without installation (it remained on the old hard drive after the upgrade), and no bugs were found.
Vista Ultimate