64 bit OS and VPN software
Solution 1:
I had the exact same problem with using my works VPN. The cisco client was then only 32bit.
I found the NCP Secure Entry Client works perfectly on Vista 64bit.
It did take some experimentation with a few configuration settings to get it running. But I've been using it now for more then a year, and can recommend it.
Solution 2:
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.
Solution 3:
I've used the Cisco VPN client software in a Windows XP 32-bit VM running on VMware on a Windows Vista 64-bit host. The VPN software works flawlessly, and never complains about not enjoying itself :-) In fact, if I couldn't get the VPN client to work reliably in the VM, I wasn't about to upgrade my main PC to Vista 64-bit. But it worked, and I did, and now I have 8GB RAM.
The other issue running the VPN in a VM solved for me was that I could never print to my network-based printer when I was connected to the VPN, since the VPN client insisted on turning off access to the local network whilst VPN'd to the remote network. Now, I can print to a local PDF or XPS printer in the XP guest OS, copy the file to the host Vista OS, then send the file to the printer.