Barbara – I’m not 100% sure what you are asking. Do you want a dropdown which only features categories on the top level and has their sub-categories in the dropdown, with futher nested categories in the flyouts to the right?
If so, then the following code should do the trick:
[code:2wt6k0sf]<ul id="suckerfishnav"><?php wp_list_categories(‘title_li=’); ?></ul>[/code:2wt6k0sf]
There is a demonstration of this on the demo page near the bottom.