Well, you could try AntiFreeze, a program of last resort by Resplendence Software Projects. Given the circumstances under which it will be invoked, the program wisely promises that it is not guaranteed to work, but it does give you a second chance. When invoked via ctrl-windows-alt-home, it suspends all active processes except those essential for Windows, giving you the chance to shut down whichever process has locked your system.
I was able to test the basic interface, but could not find a way to "force" a hard system freeze. The suspend/resume function of the program does work as advertised, however. Since it is free, I see no reason not to install it and check it out, especially if you have consistent freezes which nothing else will let you get out of. It might work, and you're not out anything if it doesn't. p
Note: My system obligingly crashed and locked itself after this review was posted, allowing me to verify that Antifreeze could stop a process when Task Manager couldn't. At least in this case, full functionality was restored.(12/02/2008)