Right goto either www.clrmame.com
and download one of the rom managers (Clr is the best imo, but others like rom centre/rom manager)
and download the dats for the renamer you have just downloaded.
Now you'll notice the dats are split for example Amiga Games #-A so the common sense thing todo is create a folder with the same name as the dat and then REBUILD into that folder or RENAME into that folder (Depending on which rom manager you are using).
Now you'll find it easier to manage the sets, which is alot if you maintain all the different dats
hope this helps