In the reports menu, there is an item called "Portfolio". If ya click on this, ya get a screen which enables you to enter yours (and a partners) income. Then press "specify properties" down the bottom and add the ones u want to the right hand side pane. I'm assuming here you have already saved both properties before hand.
If u click done it takes u to a screen which shows the analysis of both properties combined.
-Hope this helps.
Dave