How do I remove a remote access trojan?

Every night around the same time, usually between 7 - 9 pm for the last 2 days, the cursor on my screen (Windows XP) begins moving on its own.  It does not open up any files, it just darts around the screen randomonly in all directions.  Sometimes it will open the menu which is done by right clicking in the destop space.  One time I opened notepad and typed "Please stop this", immediately the cursor right-clicked and clicked undo.  But most of the time it darts around the screen randomly without a sense of purpose.  Many times it will select icons and deselect them.  It acts more aggresively when I attempt to open up applications and especially when I try to click on something or type, it will move aggresively in another direction.   I have an optical mouse that has a wired USB connection to my desktop computer.  I have cleaned the laser, and I have even lifted the mouse off the counter and still the cursor darts around by itself.  I have run spyware doctor and anti-virus software and disinfected quite a few viruses and spyware but still to no avail.  

How do I get rid of this trojan.  I feel as though someone is actually logged into my computer and monitoring what I do and maybe has keyloggin software that they're using.  How do I get rid of this spyware without having to re-install windows or format the hard drive?  I could do a low-level format after backing up my information and then re-install windows and all my software with their various serial numbers, but I REALLY want to avoid that.  

Any help would be greatly appreciated.  Thanks in advance :)