Combine 2 header files to one file

I have 2 files [login to view URL] and [login to view URL] When a user is logged out the [login to view URL] shows as the header for all pages and when user is logged in [login to view URL] shows as header for all files. I want both of these to be combined into one [login to view URL] file, and be able to get the same changed effect in header when logged in and logged out. Please accept only if you have fully understood the requirement. feel free to ask for clarifications before accepting if required.