Mindscape LightSpeed is an o/r mapper for .NET that supports full text search (via Lucene but extensible so you could add your own).
It also supports LINQ, has a Visual Studio integrated designer with full schema round tripping so you can work model-first or database-first - whichever takes your fancy :-)
There is also a free version that you can use to decide if it is right for you.
I hope that helps.