Do you specifically need the NT4 driver?
You would be better going with the 2000 driver:
http://www.hp.com/cposupport/swindexes/hplaserjet10807_swen.html
This is for the base 4050, if you need the letter specialty search for the 4050 and you will get a page that will link to the printer drivers.
If you need the NT 4 driver for an older system to use the print server, you should be able to load the Win2k driver and then add the NT 4 driver as a secondary. I don't have a server in frontof me to confirm this, but check out:
Installing Cross Platform Print Drivers in Windows NT 4.0/2000 (Q154291)
http://support.microsoft.com/search/preview.aspx?scid=/search/viewDoc.aspx?docID=KC.Q154291%26dialogID=9301228%26iterationID=1%26sessionID=anonymous|8224642%26url=
Sorry the link is so long, if you search the MS knowledge base for the Q article it is easier to find.
Hope this helps,
Jay