Set an OnObjectModify script trigger on your field that the drop down is on to run a navigation script.
You can set script triggers on an object in layout mode by right clicking the object and selecting "set script triggers"
The navigation script you tie the trigger to should look something like:
if ( table::navField = "layout 1" )
go to layout - layout 1
Else if (table::navField = "layout 2")
go to layout - layout 2
else if (etc..)
Thanks..Mike this helps alot!!