world wide web service dropping

A client of mine has a web server. It's (unfortunately) running Windows NT 4.0, with IIS 4 (I believe).

The World Wide Web Publisher service has been dropping unexpectedly on it, a couple of times a week at least. Now, the frustrating thing is, that it doesn't show up in event viewer, so it's been hard to trouble shoot. Any ideas on why something like this might be happening? Or where I can look? Or what information I can post to make troubleshooting easier?

Thanks

bmp