Load Balancing

I am currently involved in a project which is using a web application (.Net) across several servers accross 2 sites. We are expecting to be able to handle 20,000 RPS and to balance those accross all of the servers it is proposed to use Windows 2003 NLB. There are a few of us who recommend and would prefer Hardware load balancers but they are sticking with NLB. Can you point me to anywhere that would sway me one way or the other as I think at the volumes we are talking about we need to get it right.

Thanks

James