The skillbuilders modal plugin has been around for several years - there was definately a version before 4.2 - why do you ask?
Assuming you are using the Skillbuilders plugin, you would set the size of the modal in the dynamic action that you create to display the modal.
For example, create a DA on your page with the following:
Selection Type: Button
Button: <Pick one of your buttons you have previously created on the page>
Condition: No condition
Action: Skillbuilders Modal Page (2.0.0). [Plug-in]
Then in the settings you will see a Dialog Height/Width Mode. This can be set to Auto, Static by percent of window, Static by pixels.
The auto option does not work so well in IE7 (or later versions of IE if running in compatibility view).
Does that answer your question?
I'm talking about the built in modal featured in this sample app where you simply set your region template to 'modal region'
I deleted my own above solution, only the scrollbar showed up. I still cann't resize this region.
In the example app you linked to above, the edit buttons in the table do something like:
You can add in a jQuery .width to set the width of the div as follows:
This worked when I edited the page using the Chrome developer tools so I assume it will work for you.