I have to agree with those who have asked for the version of SQL Server to be specifed in future. SQL 2008 clearly states a value of 0 as the "never time out" value; SQL 2000 and 2005 state a value of blank or greater than 0.

It's surely not a surprise that the majority of those who answered this question assuming that the unstated version meant the question referred to the latest version of SQL Server?