Service Pack 2 for Windows NT 4.0 has a bad bug in it. Under certain circumstances in Remote Access Service (RAS) you can connect but cannot get any data in/out.
There is a Hot Fix available form Microsoft. It is not thoroughly tested but it does work. There may be problems with PPTP or other things but it is worth a try.
I am using MS Proxy Server & the Hot fix (after much trouble) took care of the problem. Look at the MS News Groups for more info.
BTW, MS Proxy is pretty kewl. Using it right now & see no speed drop.
Tom