You could query the tabmodules table.  It defines those relationships

mj

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Michael Jackson
Brillnat.com
Custom module development
Database access tokenized HTML modules

This is 4 years too late :) but I'm sure after the time I spent tonight this will save someone else some sweat.  There is no other way than SQL to do it just by ModuleID but if you know the Friendly Name, you do it as below:

Just create these objects:

private int intModTabID = -1;
ModuleInfo objModuleInfo = new ModuleInfo();
ModuleController objModuleContr = new ModuleController();

And then in the appropriate method do this:

objModuleInfo = objModuleContr.GetModuleByDefinition(PortalId, "UserReg");
intModTabID = objModuleInfo.TabID;

string strRedir = Globals.NavigateURL(intModTabID);
Response.Redirect(strRedir);

In this case I wanted unbreakable code in case someone changed the name of a page or removed and replaced it.  In this case we know only one module will be installed so this yields the right result.

-- Postal Mike