Your best bet with 2k is to use alt+F4 (close active program) and ctrl+F4 (close active window within programs), and just repeat alt+F4 until you get everything closed. If your client keeps a lot of windows open then that could be a problem as could (depending on the accessibility issues) pushing alt and F4 at the same time. I found a couple of programs (nothing real good - if you look hard there may be something better) on download.com that might be worth a try...
There is a program that is really not designed for accessibility issues but more for security/someone is looking over my shoulder type things. The program is called Dreadlock Privacy. I havent tried it but it claims to have a user programmable hot key that will close all open windows/programs.
CloselEx is another one will close all Internet explorer windows but that's it.
There's a program Winshutdown that assigns shutdown, restart and logoff to the F keys of your choosing.