Is there a tool to convert a large number of excel files into tab delimted files automatically?
I don't think there are any good free tools to do so right now, but you could look into using the Open Office API to write something,
Or for a quick and dirty solution, you could record and Open Office Calc macro that would do it, and launch that macro from the command line.
This might also help http://dag.wieers.com/home-made/unoconv/
convert to csv, and maybe replace , with tabs?
I just through this together, its not pretty but should do what you need. Tested on WindowsXP / Office2007.
download from: http://www.filedropper.com/xl2tab
Extract the xl2tab.vbs file to the directory containing the excel files and double-click to run. It will place the converted files into a new directory called "output." The original directory-structure remains intact within the output folder.