As they say, there is more than one way to skin a cat (no pun intended). If you are attempting to navigate to the current tabid (which you are not, it seems) you would do either TabID (from PortalModuleBase) or ModuleContext.TabID (also from portalmodulebase). When you are attempting to find a different page, you have some options and it varies based on the full story. My advice, though, would be to add a module setting to your custom module that stores the page. In the UI, you can have a drop down list (populated w/ site pages, from a core TabsControllers method) or use the URL Control in the core. I suggest this route because the tabid (which is what you would store) would be in your cached module settings (and thus you wouldn't have to look anything up repeatedly).