| Tonydd |
As to the real reason you can't use Vital Strike with whirlwind attack, is because Vital Strike is used as an "attack action" which if you look up the different types of standard actions, it's on the list. So a Vital Strike is a standard action, which is also the reason why you cannot cleave and vital strike, because they are both standard actions.
As to trip with whirlwind attack, a trip may be used in place of an attack. So yes, you may trip everyone within your reach with a whirlwind attack. Although I'm fairly certain the way Whirlwind Attack is written, it means you would lose any attacks of opportunity granted by Greater version of improved trip. Although once they try to stand up on their action, you get some AoO's then.
Hope that helps.
thank you both for the input, that clears things up very well.