Sytstem command and win2000 problem

Hi

When I run a script in maya3/win 2000 using a system command I find that a process called ntvdm.exe has started. This process does not close down and uses 100% of the CPU - I have to shut them down using the task manger.
Not only that but the system command ie a dos 'dir' command does not return any value to the string.
Anyone have any ideas.

Cheers