Currently, the software allows you to choose between 250mV and 2V on the amplitude levels. A work around for this, to get lower levels is to use the arbitrary waveform generator function.
For example, with the amplitude set on 250mV and the min at -1 and the max at 1 you will have a pk-pk output of 500mV ~ the same as when using on of the default waveform types. Now if you lower min to -.5 and the max to .5, you will have a pk-pk of 250mV, -.25 and .25 would give you 125mV pk-pk etc.
Using this method you can get down to the lower mV range. Another option to get to the low mV range is to use a 10:1 probe which will divide the signal by a factor of 10.
Crag Technologies, Inchttp://www.pc-oscilloscopes.com