Without going into the details - it's pretty self explanatory how you should add a VPN connection - I'd like to note a required setting, which is not really documented anywhere:
When you've added the connection, entered your username and password, click Advanced, and check Use Point-to-Point Encryption (MPPE) on under Security and Compression.
Withouth this setting on you may get entries in your syslog like:
- LCP terminated by peer - MPPE required but peer negotiation failed
With this, the Ipredator VPN works like a charm.