CodeGear offers a free ADO.NET 2.0 driver for registered users of InterBase here:
http://cc.embarcadero.com/item/25497
Note that "registered users of InterBase" includes the free InterBase 2007 Developers Edition. The download says that it's for 2007, but it works fine with InterBase 7, and the InterBase team at CodeGear has told me that they have no problem with people using it for that purpose.
I do not recommend using a driver designed for Firebird, as InterBase and Firebird have somewhat different SQL syntaxes, and differ in other features, as well. In particular, I think that using any driver dependent on fbclient.dll with InterBase is outright dangerous.