Actually, if you can see inside it and you haven't specifically set windows to treat vl2s as archives, you've probably saved the file as a .zip (Internet Explorer loves to do this). What you'll need to do is go into a folder, click Tools > Folder Options..., click the 'View' tab, and scroll down to the line 'Hide extensions for known file types'.
Uncheck this, press OK, and you can make sure the file is a vl2 and not a zip.
If you continue to use IE to download vl2 files, you should make sure you use "Save as..." and select "All files" under the type selection, or else it will try to name it a zip file.
Comments
put it in your Tribes2/GameData/base folder
if the map is a bunch of files like.. GenericMap.Ter or GenericMap.Mis or GenericMap.Spn
GenericMap.Ter & GenericMap.Spn - into your Tribes2/GameData/Base/Terrains folder
GenericMap.Mis - into your Tribes2/GameData/Base/Missions folder
if that doesn't work, repost with what files you've downloaded exactly, and where you tried to place them.
so yah, place it in base folder, and everything should be golden.
Uncheck this, press OK, and you can make sure the file is a vl2 and not a zip.
If you continue to use IE to download vl2 files, you should make sure you use "Save as..." and select "All files" under the type selection, or else it will try to name it a zip file.