Yes regulate is the correct word. You are running in to ohms law. While under no load your resistor voltage divider works the MSP430 draws current, and thus effectively changes the resistance of your voltage divider and lowers the voltage. While you could adjust the resistance values a voltage regulator is a better bet. However rather than an lm317 (which will certainly work) I'd suggest an ldo 3.3V regulator (ldo meaning low dropout so that it will work from the 5V input supply). The advantage being that you don't have to set the voltage as you would with an lm317. I couldn't find (on a brief search) 3.3V ldo regulators on kynix.com but digikey.com has lots of them however.
(edit:) One more thing to watch out for: if you have 5V logic or sensors (running off the 7805) it looks like the MSP430 isn't 5v tolerant so you would need level converters for any 5v level signals you want to put in to the micro.
Peter
