Although I have a mouse with my laptop, I sometimes just use the touch pad if I'm not going to be on very long. With the touch pad being, well, touchy, I experimented with keystrokes.
I found that the laptop (with XP Home) will shut down if I press "Alt+F4" keys, then the "U" key for shut down. I tried it on my desktop (with XP Pro) and it worked there too.
If it doesn't seem to work, click somewhere on the desktop and try again.