I have a Analogue devices AD557 DAC. Can I configure it for a 0v-Xv (approx 5v) output? I cant make much sense of the datasheet.

Haven't read the datasheet, but the spec says 0..2.56V output. So, you need an amplifier with a gain of 5/2.56 = 1.95 to get 0..5V.

It says on the data sheet something about adjusting the ouput gain using two pins with a resistor. I think they are connected to V- on an internal op-amp.

It says something about a "small increase" - I don't think nearly two fits in there.

Ok, looks like this wont really cut it for what I want. Maybe someone can recommend me another IC for this.

I need to build an analogue output for Arduino. I need to build the circuit on strip board. I would also like the output to be relative too a reference voltage. I have a slightly variable 5v power source, so say its supplies 5.5v I would like the maximum output of the DAC to be 5.5v.

You need a Rail-to-rail opamp (or DAC).

Do what AWOL said and just use an opamp with a gain of 2, this thing should work fine. You could even probably get away with a BJT common-emitter for this.

Whats the "reference voltage" you're talking about? Ground (0V) is a nice reference.

Also what resolution do you need? 8bits @ 2.56v max -> .32V / Bit resolution, whereas an 8 bit 0-5.5v DAC -> .687V/ bit

What I mean by reference voltage is for the binary value 0-255 I want the voltage output to be 0v - vRef. So as vref changes the value that the DAC outputs for a given binary value changes.