I recently been having trouble with my computer operating unusually. I ran a scan with Kaspersky IS 2009 and found out I have a trojan- HEUR:Backdoor.Win32.Generic. Can some one please help me get rid of this and get my system running normally again!

I have a Dell Dimension 4400 running Windows XP SP3

I know more info is needed before you can help but its a start.