I plugged in a used optical mouse and now when I move the mouse up and down.... the crusor goes right to left and moving the cursor right to left moves the cursor up and down. Wierd.

this can happen if you have your screen set to be at a different rotation then normal. I can't give you exact step by step because i don't know the display card you are using. If you have the Nividia chipset, and have the Nividia Display program, then I can find the option that needs to be changed by following these steps: 1) Right click on the desk top 2) Select properties. 3) go to the settings tab 4) select advanced. 5) the name of the graphics card (mine was a tab called "GeForce FX 5200") 6) the side-tab called "NV Rotate" 7) choose a rotation that will fix the mouse problem. I have mine set to Landscape (0 degree rotation). Hope this helps! George Please respond after you have solved your problem to notify who helped you and what solved the problem. Both sides benefit when you do.