It tends to work better if you just search for the song title. also, if the song is on an album ...you can research on google .... search the album.
Putting in artist and song together does not work well. That's just the way it seems to work...not perfect, but you learn the best search methods with time.
There is a sticky at the top of one of the forums, I forget which, called "How to find music" That will give you lot's of useful hints
ah this is the link:
http://www.gnutellaforums.com/showthread.php?t=56904
Also you will see all the other stickies which are an excellent reference