UPDATE - September 15 - thanks to 'Ed', I have it all working. Please see the comments for the answer...
UPDATE - August 14 - the VPN package linked below doesn't seem to update resolv.conf, so I stopped using it and went back to vpnc from the command line. Please do leave a comment if you're able to get all this working properly!
As I've previously mentioned, I'm running Ubuntu Dapper Drake on my laptop. Everything has been working just dandy since I recovered from my hard disk crash, except for one minor annoyance: the version of NetworkManager in Dapper Drake doesn't do VPN.
I've been using the command line vpnc to connect, which works ok, except that, when the DHCP lease expires, NetworkManager overwrites the VPN's version of /etc/resolv.conf, so I have to either keep a backup /etc/resolv.conf to copy back, or just restart the vpn.
I finally got round to googling for an answer tonight and (on this page) found a VPN package for NetworkManager on Dapper. It seems to work fine. The one niggle was that, after configuring the VPN connection in nm-applet, I had to restart NetworkManager, but that's a one-time thing.
Roll on Edgy Eft!