NTVDM running wild

I have an NT4.0 box that has a problem with the VDM process running away. Whenever I try to install or uninstall a program on this box the VDM process takes off and consumes 99% of the processor and nothing else can start. Task Manager will not stop the process; I have to reboot to stop it. I have had this problem in the past and have been able to fix it with a few tweaks. So far I have shortened the path statement to SystemRoot%\system32;%SystemRoot% and installed SP6a with no luck.