Thanks to Juerg Reimann and Nathan Mercer for the tip: Microsoft has released a Windows NT 4.0 Service Pack 3 hot-fix that fixes a problem with Internet Information Server 4.0. Imaginatively titled "iis4-fix," this hot-fix prevents a problem that causes time wait states to exceed four minutes under stress. Microsoft recommends you install this hot-fix only if you are experiencing this exact problem; refer to the README files for more details.

You can download the fix from the Microsoft Web site