trackpad stops working on 2009 Macbook Pro
A great way to rule out hardware versus software issue is to create a new user and see if the problem still occurs when logged into the new user. 

System Preferences>Accounts> + (may have to unlock first). For ease of use, I'd make the new "test" account an administrator. When you are done, log out and back into your regularly used account. System Preferences>Accounts> - (delete home folder and all contents). 

If the issue persists, it should be related to hardware and not software.

Hope that helps!