5v to 3.3v resistor

Can anybody recommend a good 5v to 3.3v resistor for using a duemilanove to send serial commands to an ipod? I'm not sure exactly what type I would need.

You may need a voltage divider, like the one shown here (used for an SD card): http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1206874649/8