Which VPN do I use for a Cisco VPN concentrator?
With a "really old" Cisco VPN concentrator, there are pretty good odds that you can get by with a PPTP tunnel. Especially if you're relying on the native Windows client from desktop/laptops (XP?).

However, with Exchange in the mix you may not need to establish a VPN. My new employer runs exchange and I'm using the "Mail" app to connect to it with no fuss or muss. It "just worked" after I plugged in the external mail server address (mail.mycompany.com) and my domain creds.