If you are saying you want staff to see the website before they log on to Windows (see their desktop) then this is not possible (unless you boot from a disc maybe).
You could run a script which executes at log on which automatically loads the website but the user could always just close it.
Either way, how would the user get from the browser back to their desktop? Would by closing it allow the desktop to then be shown? Unless you have staff log on to the website as well for authentication to track that they visited the site, but this still doesn't mean they will have actually read the site! Even if the website loads as they log on, is the website changing every day because if not, you won't want this to occur every day (staff will get annoyed). So will this mean you run it once a month, or just at times of updates? :)
This entire thought and request is quite insane! Sit down with your boss at once and explain why they should not be making any more decisions!