is there a way to set a different alert for sms messages from different contacts instead of just one notification for all sms messages?
Android leaves a lot of that sort of functionality open for third party software. Good and bad, but in this case good.
Download Handcent SMS from the market. It's free. It's a complete overhaul of the stock Android messaging app, and one of it's features is the ability to have custom ringtones and vibration patterns fro each contact.