You might want to try using a Data List as the dropdown part of your combo box component. This isn't a complete solution, but it might be good enough for a prototype, and a developer in Flash Builder can easily turn it into the real thing.
Hey kk88, I just checked out your FXP file and it looks like you're doing what Adam suggests. If you really need 100 rows I'm not sure how well that's going to work in this beta of Catalyst. We haven't done much in the way of optimization.
Is there a reason you have to be able to prototype with 100 rows?
I don't have a requirement to prototype 100 rows but my point is that the current approach is painful to develop for even 10 rows. I guess I just have to be patient for a future release of catalyst where combo-boxes will be available as part of the standard set of components.
On the same note, I want to let you know that the Expedition_Simple.fxp file that is part of your Catalyst tutorial (http://blog.digitalbackcountry.com/2009/01/getting-started-with-flash-catalyst-tutorial/) does not open in the beta 1 release of Catalyst. I get the following error message when I open the file: "Flash Catalyst cannot open this project because it was created by an incompatible version of Flash Catalyst". It will be extremely helpful if you can upload a new copy of this file.
Can you tell us what is painful about prototyping a dropdown with just 10 items? If you're using a Data List for the dropdown part of the combobox, adding 10 items to the design-time data collection should be easy...
The tutorial you're having trouble with is for an older version of Catalyst -- in addition to the file being incompatible, some of the steps won't make any sense in the beta either. If you're looking for good tutorials for the current beta version, I'd suggest http://labs.adobe.com/technologies/flashcatalyst/tutorials/ as a starting point.