X-axis in milliseconds

Hi,

I have data files of voltage signals captured by a digital waveform 
recorder. These consist of a single column of values sampled at regular 
intervals. I can easy plot the signal showing voltage against sample 
number but what I want it to show voltage against time in milliseconds.

The time between samples is known (e.g. sampled every 1.2ms). Is there a 
way I can rescale or recalculate the X-axis to show time in milliseconds?

MW