vpnc_0.5.8-0m5_armel.deb from extras-devel worked for me perfectly (never used the gui), but you need to be aware of the fact that when you install it, it hacks the file /etc/udhcpc/libicd_network_ipv4.script. Even if you uninstall the package before the next firmware upgrade, it can cause problems if the next firmware needs changes in that file, because having touched that file it won't get upgraded. This is what happened to a number of users from PR1.0.1 to PR1.1.

juaalto described his solution to that issue here:

http://talk.maemo.org/showpost.php?p...8&postcount=41

but that resolves the issue only if you have vpnc installed before the upgrade to PR1.1. A fresh installation hacks the mentioned file which could (potentially) introduce a problem for the next upgrade.
Also, it's hard to foresee whether the above solution remains correct forever in any future firmware.

Unfortunately, vpnc seems to be orphaned for the time being. It would really be great if somebody who is an expert brings it in line with how things work in the N900/PR1.1. I've filed a bug report on garage.maemo.org, but so far I've not seen any activity.

EDITS (02-01-10):

1) It seems that vpnc is not orphaned, but somebody is working on it: today vpnc_0.5.9-1m5_armel.deb appeared on extras-devel. I haven't installed it, but just looked at the package, and found that the above-mentioned fix by juaalto is incorporated, and that the package post installation script even cleans up the incomplete upgrade from PR1.0 to PR1.1 when the previous version was installed. However, I guess that all afflicted users will have done that already themselves.

2) In the meantime I have found a possibility for using vpnc without having to deal with the package from extras-devel, which still comes with big warnings "This package is not using one of the allowed user/* sections!" and even "missing dependencies". I have Easy Debian installed, and found that I can use Easy Debian to have the original Debian package vpnc installed without having to tamper with Maemo. See: http://talk.maemo.org/showthread.php...275#post496275
So until the Maemo version of vpnc makes it into Extras, I'm using this alternative (from the commandline), which I judge to be much safer. It works perfectly for me, be it with WLAN or G3.