CiscoSecure or Microsoft IAS

We are in 2000 Native mode and our users currently dial in and get authenticated by a Cisco 3640 Router/Access Server. What I would like to do is either use a product like CiscoSecure or Microsoft’s IAS so that users will get authenticated against Active Directory. This will also help with maintaining user accounts. Has anyone compared Cisco’s solution vs. Microsoft’s? I am a Cisco guy so I have more knowledge of their product. Any help would be appreciated. -Severini