Y'know, this really isn't a SilkTest question...yet. Remove the tool from the equation and figure out what you need to test first. It doesn't really matter if you're using SilkTest or WinRunner or SAMIE. What you really need to do is to talk with your development team to understand if any changes were made other than the web server. Depending on what was changed, that will help drive what you need to test.
Something else to keep in mind is your existing SilkTest scripts. You should be able to run most or all of them without changing anything.
"The single biggest problem in communication is the illusion that it has taken place."
-George Bernard Shaw, Irish playwright and Nobel Prize winner, 1856-1950