The scroll wheel is probably just dirty.  A tip that I picked up in another thread was to turn it upside rub the scroll wheel around in all directions a few times on a 
clean sheet of paper (does that make sense?).  I did that, except on my mouse pad and it worked.  Only the thing was clogged up again in no time.  I have since bought another mouse that doesn't suck.  There are a number of threads regarding people's favorite mice.  
My advice is, just keep cleaning it as needed or get a better mouse.
Tata
