Hardware Interfacing Rules - Arduino to RS232 Devices

I'm new to Anduino but experienced with other micro controllers & are waiting for delivery of my first 2 Anduino units.
My interest is interconnecting Anduino to other RS232 serial devices like a COM port on an old PC or typical USB/232 adaptors but there does not appear to be a definative explanation anywhere on how this should be done. Prime concern is that a 232 device could be working at +/- 12 volts (think IEEE spec even allows 15 volts) but this will no doubt cause grief for a TTL voltage level device if directly connected.

The obvious solution is to use a MAX232 IC as an interface but unless I've overlooked it my web search of this forum have not identified any recommended method supported on this forum. Following is the type of thing I'm expecting:
http://chuckontech.com/?p=147
http://avrprogrammers.com/doc-max232-arduino.php
Hope this is of assistance to others....

Both schematics will work. You'll have to get the cap values from the ChuckOnTech if you wanna build the MAX232 Arduino one.
but if you look around, there are MAX chips that don't require the caps; they're built in. DigiKey should have the part, off hand - I don't know which one it is, but I'm sure someone else will know.
And if you still need D0 and D1 for USB debugging, you can use any other D pairs to connect to.