Since Cisco's VPN client doesn't even work reliably on a 32-bit system I have been exploring other alternatives recently. I didn't try the NCP Secure Entry Client because of cost, but the Shrew Soft VPN Client is a cost-free alternative. It is a little hard to set up and may require a little experimentation, though.
I endured a little pain in using a FreeBSD VM with vpnc to route my host system through. Wasn't suitable for what I was doing, though (latency kills playing games, unfortunately [yes, I know, I should be working ...]).
ETA (2009-11-16): The Cisco AnyConnect client apparently works even on 64-bit Windows and is at least compatible with some older VPN concentrators. However, I had some issues again on Windows 7 32-bit where it sometimes connects and sometimes refuses to, even though the "normal" Cisco VPN client works fine.