Connectivity issue - SQLServer not listening on port 1433/ms-sql-s

Hi. I'm a SQL Server novice, so apologies if any of this sounds simple.

I am running Windows XP SP2, and have just installed SQLServer 2000. I
need another application to connect to SQLServer, and am specifying it
to do so via localhost:1433, but keep getting an error whenever I try
doing so saying it cannot connect to the database. A colleague of mine
has the exact same set up on his machine, and he can connect to SQL
Server fine. Running 'netstat -a' at the command line on his machine
reveals that the system is listening to port 1433/ms-sql-s. Running
netstat on my machine shows that the system is not listening to
1433/ms-sql-ms. I have checked in Network Config in SQLServer
Enterprise Manager, and TCP/IP is set to be using 1433.

To confirm this, my application can connect over the network to my
colleague's SQL Server. but he cannot connect over the network to mine.

So I'm pretty sure the issue is related to this 1433/ms-sql-s problem.
Does anyone know how to resolve this? Many thanks.I just installed SQL Server Service Pack 3, and the problem is now
resolved. Perhaps it was related to the Slammer worm.