I've been doing it for years - using your example I can show you basically how to do it. I have several domain names sharing one website all with entirely different content, design and layout. (Helps with global file sharing.)
Select Case Request.ServerVariables("SERVER_NAME")
Case "
www.test1.com"
Server.Transfer "/default.asp"
Case "test1.com"
Server.Transfer "/default.asp"
Case "
www.test2.com"
Server.Transfer "/test/default.asp"
Case "test2.com"
Server.Transfer "/test/default.asp"
Case Else
Server.Transfer "/pickadomain.asp"
End Select