You need to be a bit more clear on this..

Encrypted string in an application and building a connection string?

- decrypt password, build unencrypted connection string use that to connect.

Connection string is encrypted in config file and you need to use it?

- read encrypted data, unencrypt and use it.

Either way, you need to build a class to handle your encryption requests, and your connection string you use needs to be clear text. Ado and OLE drivers cannot handle encrypted strings. There are new methods in .net2 to keep your connection string encrypted in your config file.