Hi
I can recommend at least two FAQs on
TalkOrigins Archive: Exploring the Creation/Evolution Controversy
Radiometric Dating and the Geological Time
Scale
Is about dating, and
Isochron Dating
is about isochron dating methods. Now these methods assume that the rate of decay has remained constant. Contamination can be identified with almost certainty, and the initial amount of isotopes need not be known (in fact the methods calculate the initial amounts!)
I like the second FAQ, very much, and have never seen any YEC even trying to argue against these methods.
If you need more info, the pick up a copy of Dalrymples
excellent book
Dalrymple, G. Brent, 1991. The Age of the Earth. California: Stanford University Press, ISBN 0-8047-1569-6
Cheers
/Sren