NCP Secure Entry Client should do the trick. I have not used it in Windows 7 (the maker says it works), but happily use it under Vista 64. It is a little pricey at $144/client. If this is for more than a few users, it might make more sense to upgrade your Router/Firewall so you can use the still maintained and supported AnyConnect client from Cisco.
VPNC with the VPNC Front End works on 64bit Vista according to various web searches. I have no experience with VPNC under windows, but am happy with it under linux.
Many Cisco Firewall/Routers can be configured to support the built-in l2tp VPN client that Vista has installed by default. I have connected to this type of setup as a user but know nothing about the setup from the router/firewall side.