<p>I started a project a long time ago and created a <strong>Data Access Layer</strong> project in my solution but have never developed anything in it.  What is the purpose of a data access layer?  Are there any good sources that I could learn more about the Data Access Layer?</p>

I recommend you read up here:
http://msdn.microsoft.com/en-us/practices/default.aspx
Using a DAL will help you isolate your data access from your presentation and business logic. I use it a lot so that I can easily swap out (through reflection and dynamically loading assemblies) data providers.
Read up, lots of good info there.
Also, look into the
Data Access Block
if you are planning on using .NET. It can be a big help.