Beaded dress is doable; but it would take a lot of work, with many hours evolved.
Now I have never done one, a dress; but I have done bead Embroidery using seed beads and bugle beads
I used a back stitch on my work which on dresses I don't think is normal. I believe a running stitch is used.
Years ago I belonged to about.com beadwork forum no longer there
and a gentleman from another county posted showing his beaded bathing suit no cloth used and claimed they the suits would not ravel if a bead was cut out. I think he had the suits done with a repeat square stitch or something like it.
Back to dress beading; You might check out some sewing couture books see if there is information on beading in any of those books. I think you will need to add a backing to the cloth you use for the dress to add stability if you plan to do heavy beading a more solid beading others than a few beads here and there.
Also you might search http://artisanssquare.com/sg/index.php
a fantastic sewing forum.
Hope this helps!