I've been unable to use a VPN connection to my work computer since I upgraded
my home box to Vista. The interface opens but I get a "could not connect to
server" pop-up and a "disconnected" message on the VPN page. I have settings
the same as I did on XP, but no luck. Any suggestions.

New Cryptographic Support L2TP/IPsec-based VPN connections now support the Advanced Encryption Standard (AES) with 128 and 256-bit keys. Support for weaker cryptographic algorithms—40 and 56-bit MPPE for PPTP and DES with MD5 for L2TP/IPSec—has been disabled by default.

To enable 40 and 50-bit MPPE for PPTP-based connections and DES with MD5 for L2TP/IPSec connections, create and set the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Rasman\Parameters\AllowPPTPWeakCrypto registry value (DWORD) to 1, and then restart the computer.

Without the registry key modification, Vista simply reports a failure in connecting and offers a diagnostics option. Of course that option doesn't find anything wrong.