Just to complete the answer:

After installing and getting pptp to work, you can use the package
dbus-scripts (see here http://www.mail-archive.com/maemo-de.../msg06634.html
) to automate connection.

Create file called /etc/dbus-scripts.d/dbus-pptp (or any name you wish in that directory) containing the lines

/path/to/pptp-start-script * * com.nokia.icd * tsunami * CONNECTED
/path/to/pptp-stop-script * * com.nokia.icd * tsunami * IDLE

(replacing tsunami with your wifi network name), and whenever you connect to the wireless network (by manually using the connection manager, or automatically) pptp will connect.