Encrypt connectionstring in web.config

You can encrypt it from the DOS prompt, if you have access to it..
c:\windows\microsoft.net\framework\Vx\aspnet_regiis.exe -pef "connectionStrings" c:\Inetpub\foldername

The key to decrypt it lies on the same machine where it was encrypted.
When your application access the connectionstrings it would automatically do the decryption.

Customise your Web.Config file

By storing unstable data (subject to change frequently) in the web.config file, you can easily make changes to the data without having to re-compile and re-deploy the program. From NET 2.0 onwards, we can make use of the Configuration Class, which reduces the hassle of using the IConfigurationSectionHandler found in NET 1.x.x.
http://aspnet.4guysfromrolla.com/articles/032807-1.aspx