I been working on two internal websites for my company. Currently I am facing the issue of combining both websites and kind of making a kind of portal. The first one users will see is a layout with an image slider of company announcements and have a top menu with some of the departmental content. The second site has a list of quick links in the form of image links to our applications and a main menu with links to forms and documents.
I guess the challenge is two have the two sites up, but integrated so that the users feel that they are on the same portal. Maybe similar to how ASP.net Master Pages work (ie., a general theme and different menus and elements) - something like this site which have different sub-sites, but is all the same concept, different headers
What I really need is advise about how to accomplish this the best way - what should I pay attention to as far as design, color matching, and themes?