You may also have to do something about "handshake".
A suggestion: It may (or may not!) help to first do some experimenting with driving your serial device from a PC. If you use Windows, Hyperterminal or PuTTY would be suitable software. This might give you "first success" with making the device Do Things, and when you've solved the problems of driving it from the PC, you could then go on, armed with some knowledge you didn't have before, to driving it from the Arduino.
There are some general notes about talking to serial things via Arduino at...http://sheepdogguides.com/arduino/art4SeIntro.htm