on a w2k system.. the folder is this :
C:\Documents and Settings\Administrator\My Documents\maya\4.0\scripts..
you place the mel in there.. and "summon" it by goin' to the Command Line and writin' it's name.. (without the .mel part)

was the mel by itself or was there some other file too..? like: *.xpm ..? 'cause if there was you should place that in the folder :
C:\AW\Maya4.0\icons..
and the mel in :
C:\AW\Maya4.0\scripts..

if it's the second case.. in maya go to :
Window > Settings/Preferences > Plug-in Manager...
locate the new plug-in and check both options boxes next to it..

hope this helps you out.. :p