Interfacing 3V TI MSP430 to PC serial port
There is no simple solution here. Really what you can do is either:

1) Use a different chip that can allow for lower voltages. Take at the list below:
http://para.maximintegrated.com/en/results.mvp?fam=rs232&amp;793=1.8|2.5|2.5%20to%203|3

2) Use some booster IC to bring up the voltage to 5V. Btw, the MSP430 won't tolerate 5V I/O very well, so you're better off using a 3.3V RS232 device at least.

Solution #1 in effect is #2 but more integrated.