You can use the OMPM's OFC.exe tool to do bulk conversions from .xls to .xlsx, but the tool is complicated to use. I don't know of any exes to convert from 2007 to 2003 format.
Manually these tasks can be performed as follows:
For #1, Open the file in in Excel 2007, click the Office button, and use the Save As command and in the Save as type box, select Excel 93-2003 Workbook.
For #2, Open the file in Excel 2007, click the Office button, and then click Convert.
Visit the Office 2010 Compatibility Resource Center http://technet.microsoft.com/en-us/office/ff460851.aspx And the Office Resource Kit Blog http://blogs.technet.com/b/office_resource_kit/