It's not too difficult if you grasp this one: check forums and wiki for the javascript-api. That's the route to follow. If you're familiar with it there's a lot of possibilities to achieve what you might want. If not.. steep learningcurve ahead.. The other path is via the workflow-engine. More difficult than javascript.
I've been taking a look to the JavaScript API and it seems quite interesting to me…
I can create a script that checks the node properties, but I could only execute this code as an action (consequence) in the rule, not as a condition (requisite)… And my intention was to check the property as a condition for the rule… =( Am I wrong?? Could I implement a new condition that test the property with the script??
Don't know if i understand you correctly but..: If you simply run the script ALLWAYS you can check your conditions within the script? So the triggers the script, the script checks and acts upon your conditions. Doesn't sound way off to me? :?