Here I go again. it's probably something simple but I can't remember how to do it.

I reinstalled PCLinuxOS with LXDE last week for reasons not related to this question. Now I have a problem with the mouse wheel changing the desktop every time I turn it. This is annoying when reading an e-mail or web page and I turn the wheel to scroll up or down the page and the cursor is just off the edge of the window. Before I reinstalled everything I could turn the wheel with the mouse on the background and it wouldn't change the desktop on me. I've looked though 3 Linux forums and searched dozens of pages in Google, all I find is how to stop this in KDE, none of which work in LXDE. Has anyone got any info on how to turn this on and off? Thank you, Stephen