If you want to access your SQL Server 2005 Express or Developer edition from a remote box you will need to make some changes in the SQL 2005 configuration. I just learned that myself - while trying to access my database engine running in a virtual machine.
I had it installed and all and everything worked fine when using SQL Server Management Studio locally, but when trying to access the database from my host machine it just timeout in the connection call.
My first test was to just ping the virtual machine - and since it didn't respond I realized the firewall didn't allow incoming traffic. After fixing that I was so sure that it should work - but to my surprise it didn't work.
Ok, fine I thought, I guess I need to read up on the sbject if you really want me to...
As it turns out, SQL Server 2005 Express - and the Developer Edition as well - by default only allows local connections. While I can understand that configuration being default, in some ways I can't. I mean considering the nature of the application - a database server - and also considering the fact that virtual machines are becoming almost a must these days. Anyway, no big thing, this article is to show you how to get it fixed nothing else:
In the menu select SQL Server 2005, Configuration Tools, SQL Server surface area configuration
Click on Surface Area Configuration for Services and Connections
Now you get this picture: 
Now click Remote Connection in the tree and: Select Local and remote connections
Now Apply, Close and restart the database engine from SQL Management Studio and you're done.
