My employer has a Microsoft VPN (PPTP) server and I finally got connected to it. The Internet Connection app allows you to access a VPN, but it has a couple of parameters that may cause problems, and it also might be useful to see the command line way to do it. I got the basic command line syntax by invoking Internet Connection, then looking at ps -axlww. Here's the command I use:
% sudo pppd serviceid 2 debug logfile /tmp/ppp.log plugin /System/\
Library/SystemConfiguration/PPPController.bundle/Contents/PlugIns/PPPDialogs.ppp \
plugin PPTP.ppp remoteaddress WWW.XXX.YYY.ZZZ redialcount 1 redialtimer 5 \
idle 1800 mru 1500 mtu 1448 receive-all ipparam 192.168.0.1 novj 0:0 noipdefault \
ipcp-accept-local ipcp-accept-remote noauth refuse-pap refuse-chap-md5 \
user domain\\username mypass password hide-password noaskpassword \
forcedetach mppe-stateless mppe-128 looplocal
% sudo route add -net AAA.BBB.0.0 AAA.BBB.CCC.DDD
Where you replace 'domain', 'username', 'mypass', and the 'AAA.BBB.CCC.DDD', etc, IP addresses with the proper ones for your site.Mac OS X Hints
http://hints.macworld.com/article.php?story=20030311232930261