If you'd like to connect to a Windows PPTP VPN here is a howto to make it happen.
You need to have Ubuntu 10.04 if not you need to apt-get some packages that are not installed by default.
- Click 'System' -> 'Preferences' -> 'Network Connections'
- Click the 'VPN' tab
- Leave 'Point-to-Point Tunneling Protocol (PPTP)' selected
- 'Click Create...'
- Type in a connection name and check the box below it if you'd like the connection to connect automatically
- For 'Gateway' enter in the VPN hostname or IP IE vpn.contoso.com or x.x.x.x
- For the username type in DOMAINusername where DOMAIN is your Windows domain name and username is.... your username
- Type in your password and leave the 'NT Domain:' box empty
- Click 'Advanced...'
- Check 'Use Point-to-Point encryption (MPPE) and leave 'Security' on 'All Available (Default)'
- Check 'Allow BSD data compression'
- Check 'Allow Deflate data compression'
- Check 'Use TCP header compression'
- Leave 'Allow stateful encryption' and 'Send PPP echo packets' unchecked
- Click 'OK'
Now this will send all your network traffic over the VPN. If you'd like to still be able to use your local connection you need to click the 'IPv4 Settings' tab, click 'Routes...' and check 'Use this connection only for resources on its network'. Enabling this can be a security risk so you should talk to your IT administrator first before enabling it. That option is called split tunneling.
Now to connect left click your network icon in the panel on the top right and hover over 'VPN Connections' and left click the connection you just created.
I'm not on a connection that allows me to do further testing but when I can I'll update this with more information.
For earlier versions of Ubuntu use the following KB article to help you install the necessary programs.