Outlook saves its client-side rules definition in a binary blob in a hidden message in the Inbox folder of the default store for a profile. The hidden message is named "Outlook Rules Organizer" with a message class "IPM.RuleOrganizer". The binary blob is saved in property 0x6802. The same binary blob is written to the exported RWZ file when you manually export the rules through the Rules and Alerts Wizard.
Has anyone deciphered the layout of this binary blob?
Hmmm, that is a tough one...
Here's the server side rules protocol
According to this cryptic affair it looks as though you'll probably need to spend some time in Reflector as well...
Ah, these look closer to the mark and promising, give them a look:
Description of programming with Outlook rules
How to use the Rule.dll sample to create an inbox rule in Visual Basic
In general, Microsoft is explicitly saying it hasn't kept the documentation up on the rules in the last two versions and so the caveats...