What version of SQL Server 2005?
The reason i ask is that the developer edition e.g. is not network enabled by default so you have to enable TCP/IP and express is the same.
So if you could tell us what version that would be good.
If its developer, evaluation or express launch the sql server configuratiion manager and go to sql server 2005 network configuration and prortocols and then make sure tcp/ip is enabled. Also go to the surface area configuration tool and ensure that in the remote connections bit that it is set to allow both local and remote connections.
hth
David