I run into old OS's on a regular basis - usually for some multi-million dollar industrial system that the vendor has either gone out of business or abandoned.  For NT 4.0 complete airgapping is basically mandatory, and getting physical hardware that can run is essentially impossible, so it's one hardware failure away from a dead box.  Net: It's way past time to get off it, no matter what it runs.  Glare right back at the customer :-).  

VMWare dropped support for NT years ago - honestly, if you have it running on workstation, consider yourself lucky and use that while you can. 

There's an ancient KB article here: http://partnerweb.vmware.com/GOSIG/Windows_NT_4.html with some instructions...don't know if it'll help.   It was a pain to even install on physical hardware!