Arduino to NSLU2 via TTL (3.3v - 5v) ?

The NSLU2 is a NAS device that is often hacked - I have a few, and this article on adding a serial port - however, the nslu2 has a ttl type port like the arduino - just at a different voltage - the nslu2 is 3.3v, the arduino is 5v.

So my question is, how would I connect the two? Is it a simple matter of resistors for the 5v->3.3v?

On that page it mentions that a 5v ttl (arduino?) should be able to 'read (rx)' the output (tx) line of a 3.3v fine. That leaves the input to the nslu2 - would a simple resistor work to drop the voltage down?