Jokes

Question: sometimes cursor disappear on vista when i use dual monitor with laptop, hp dv2221
second monitor can show cursor but main monitor...
do you know how to fix it?

Jokes

And what is the video card your using???
I have seen this happen with panning accross several monitors and the mouse gets lost.
If you are switching from task to task, and sweeping your cursor across dual monitors, or even a seamless wide screen, chances are you might lose track of where your mouse is.
using two monitors you will have the physical edges of the monitors smack dab in the middle of your viewing space. The separate halves of a document opened across the great divide might not line up.
Borrowed from Keith
you'll often run into situations where windows will end up off screen and need to get them back where you can see them.
Recovering lost windows

HOWTO Dual Monitors
HOWTO Dual Monitors - Gentoo Linux Wiki