The Cisco IPSec VPN client does not support 64-bit operating systems. Your only option is the AnyConnect SSL client. Support for this client will require additional configuration on your headend IOS router or ASA.
64-bit VPN client support is added in 5.0.7, now in public beta
Key Capabilities available for Beta Testing:
New Platform support – Windows 7 & Windows Vista 64-bit platform compatibility
Software Access: http://tools.cisco.com/support/downloads/go/Redirect.x?mdfid=281940730 (under 5.BETA)
Software is available for download by any customer with a Cisco.com SMARTnet™ enabled login.
There is a free 3rd party IPSEC VPN client that supports 64-bit Windows distributions:
I've tested this numerous times with single factor and extended authentication VPN configurations on both PIX and ASA platforms.