I just posted a binary script that will do the job. Just click in a row of your table and it will split the table so that the row in which you click is the first body row of the second table. You'll get an error if you click in a footer or header row or in the first body row.
Get it here:
<http://pdsassoc.com/downloads/SplitTableAboveSelectedRow.zip>
After unzipping, put the file in the Scripts Panel folder of the Scripts folder of the Version 5.0 folder of the Adobe InDesign folder of your Preferences folder. It will appear in the User section of the Scripts Panel (which you'll find under View/Automation). Just click in your table at the appropriate place and double-click the script's name in the panel.
Dave