Josh,
I have had issues adjusting the horiz width in ES3 and ES4.
I have been able to adjust the swimlane height by clicking the swimlane and setting the property there.
The only reliable way I have found for width is to open the .process file on disk ( outside of WorkBench ), and adjust the size parameters.
These files are XML.
Save the file, and open in WorkBench and you should see the changes.
Good Luck.
Mark