I have been trying this for quite sometime as I did not want to reboot to Windows when I wanted a VPN connection. Tried a number of approaches. Many did not work (ex: installing Networkmanager-pptp and Bryan’s method using YaST). Just gave KVpnc a try and it worked the very first time! Here’s what I did.
Create a new profile in KVpnc
Using KVpnc requires you to enter the root password!

Add new profile

Click “Next”.
Type selection
Choose PPTP here

Click “Next”.
PPTP settings

You could experiment with other settings once you get a working connection.
Click “Next”.
User settings
Type in your username and password for connecting to the VPN server.

Network settings
Default is fine

Click “Next”.
Virtual IP Address
Left unchecked.

Connection status check
Uncheck everything.

Connection options
Check if you want to connect after creating profile.

General settings
Give a name and description for the profile and type in the IP address of the VPN server under ‘VPN Gateway’

Finish
Ready to go!

Note
KVpnc is still a KDE 3 application. It was available in the repos for
openSUSE. If you are having troubles connecting, have a look at /etc/ppp/peers/pptp.
Here is how mine looks.
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