<p>Could someone please explain the best way to connect to an Interbase 7.1 database using .NET/C#?</p>

<p>The application will be installed on many end user computers so the less "add-ons" that I will have to package with my application the better.</p>

Check this providers:
Interbase and Firebird Developer's for Visual Studio .Net
Firebird .NET Data Provider
FireBird - InterBase .NET (Mono) Providers