Reddit mentions of LINQ in Action

There are all sorts of resources as you have found out. I see you say 'GUI based database app' - are you talking about a desktop application or a web application? I would recommend a web interface as it is cross-platform and doesn't require install/local database/etc. Right now the newest thing (and easiest IMO) is Asp.NET MVC: http://www.asp.net/mvc I recommend this book: http://www.amazon.com/Pro-ASP-NET-MVC-Framework-Second/dp/1430228865/ref=sr_1_3?ie=UTF8&s=books&qid=1278940788&sr=1-3 (I did not read this edition, but the 1.0 edition).

You don't necessarily have to use LINQ, you can use older ADO, stored procedures, or any combination of the above, but in my opinion, LINQ-to-SQL is the easiest to work with. This is the first explanation I read of it back in the day, and it was easy to understand and got me underway: http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
There are also some good video tutorials here under the 'data' section:http://www.asp.net/web-forms
I also really liked this book when learning: http://www.amazon.com/LINQ-Action-Fabrice-Marguerie/dp/1933988169/ref=sr_1_1?ie=UTF8&s=books&qid=1278941155&sr=1-1

As a shameless plug, I also have a video course on learning how to do this at http://c-sharpener.com - but that is Asp.Net WebForms and not MVC (just another way of doing it).

If you have any more specific questions, please ask! I hope I made some sort of coherent sense?!