How to Force XP into sleep mode(3 posts)
If you look at this article, you'll see instructions for how to make an icon to put the computer into sleep mode (or shutdown, restart, etc). I'm not positive they work in XP, but I think they should.
You can then add a shortcut key into the shortcut by going into the properties. I think you'll have to logoff and back on for the shortcut key to work, but that should get you where you want to be.
If that doesn't work for you, you can create a shortcut to nircmd.exe, which can be found here: http://www.nirsoft.net/utils/nircmd.html The instructions are on that page for the corect command line argument to pass to it. You could use a shortcut key in that shortcut as well.