Does the Zan's Minimap mod work with Minecraft 1.6.6? When I try to use it it always appears to throw an error when I try to load my game (but the message disappears too fast for me to read it), and my game never loads. I already have modloader installed and I made sure to delete the META-INF file.
According to the forum thread (as of the time of posting this answer), ZanMinimap 0.9.9 (the most current version) is only Beta 1.6.4 ready.
The current version of ZanMinimap, 0.10.0, is Beta 1.6.6 compatible.
By the sounds of it you're not downloading a new version. Due to the way mods work, they need to be recompiled every update. As Kevin has pointed out, it has not been updated yet. When it is (if it is), you will have to download that file instead.
tl;dr Mods for old versions will not work for new ones unless updated.