One of the cool new features in the configuration system with ASP.NET 2.0 is the ability to encrypt any of the values stored within them (note: this works with any configuration section -- including ones you build yourself). This is obviously important when storing sensitive information like connection strings -- and now enables you to avoid having to roll your own solution.
K Scott Allen posted a super simple example of how to encrypt a section on his blog (spolier: it is a one-line command).
Here are a few other good articles I found on the web that discuss it more as well:
Hope this helps,
P.S. While I'm mentioning building your own configuration sections, I thought I'd point out this past blog post i did that references Dmitry's cool utility for building your own custom configuration sections + VS 2005 XML intellisense support for them.