Take a look of the following article which may apply to your issue...
FIX: You may receive a "SQL Server could not spawn process_loginread thread" error message, and a memory leak may occur when you cancel a remote query in SQL Server 2000
http://support.microsoft.com/kb/893312
There may not be enough virtual memory when you have a large number of databases in SQL Server
http://support.microsoft.com/kb/316749
MohammedU
Microsoft SQL Server MVP