creating Exchange DAG and CAS failover with 2 Exchange holding HT CAS and MB and one server for Windows NLB

Hello Exchange Gurus,

I am new to Exchange server, I am in the middle of the implementation of Exchange 2010 Fail-over, I have following scenario:

Server 1: CorpExch1 with HT, CAS and MB role installed

Server 2: CorpExch2 with HT, CAS and MB role installed, these both server are part of DAG

Server 3: holding DAG Witness Directory and can be used as Windows NLB server for CAS array, I did some research on Internet and found that this can be possible. But I don't know how to configure NLB for CAS fail-over for these 2 Exchange server.

any help will be greatly appreciated.

Thanks in advance