ORM Framework related

[whyvenky]

A few weeks back I had asked a question about DevForce Express (Should I use it?) in this forum. Now I have found on the internet an open source framework called NHibernate which is very similar. Which one should I use? Open source or Microsoft? Since Dot Net is Microsoft would it make more sense to stick to a Microsoft suggested product? What problems am I likely to face?

Thanks

Venky