First off, a clarification. I presume that you mean that the cursor on your screen leaps around. If your actual mouse unit is jumping then I think you might want to vacate your house or get a really aggressive cat or something. :-)
There are plenty of reasons that your cursor could be weirding out, actually. It could be as simple as you needing new batteries in the unit since it's wireless. Secondly, optical mice are very sensitive to the material upon which they sit: are you using an optical mousepad or other surface that is optical friendly?
Hmmm.... what else.... you could be seeing interference with the wireless unit. Do you have other radio or wireless units right by your computer? If you hook up a traditional wired mouse, does the cursor exhibit the same behaviors? If you move your computer and mouse to another room, does the behavior remain?
You might also want to check the sensitivity that you have selected for your mouse in the Windows XP Control Panel area. Choose Start -> Control Panel -> Mouse then go to the Pointer Options tab and see if any of those settings affect the behavior you're seeing.
Also, according to my pal Leo Notenboom, super Windows guy, it's possible that the Microsoft Speech Recognition engine has been turned on and the system is trying to interpret noises as cursor motion requests. I'd say that's a pretty unlikely explanation given what you describe but if you're still seeing the problem after all the suggestions given above, you might want to check out Why does my computer go nuts sometimes? for more troubleshooting advice.
