Basically you've got to do something wrong!
Shouldn't really happen with stock nettalk.
Sometimes it happens for me with odbc driver problems, but its a function of very high volume and high memory usage, 3+ GB RAM usage per Nettalk Server Process and MySQL ODBC 5.2 or 5.3 driver that tries to do fancy stuff with cursors and eats memory (not NT specific). It causes a database error within a thread that cannot be recovered from and the thread stalls.
Other times it happens because I have some reports that take a very long time to run - in the minutes (printing a report that consists of hundreds of pages that includes many hi res images). My customers sometimes like to keep pressing print thinking that will help the report arrive quicker. Since the processes take a long time each one knocks out a thread.