Hi,
The framework for building form importers was available in InfoPath 2003 SP1, but only now InfoPath 2007 has built-in importers. In InfoPath 2007 we have option "InfoPath importer for Excel workbooks" which is not available in InfoPath 2003. You just need to run the Import Form Wizard in InfoPath to convert your existing Word and Excel forms to InfoPath forms. When you import a form, an InfoPath form template is created and you can customize it to satisfy your needs. As we know, importing has a great advantage over copy and paste: the built-in importers will create controls and schema for you automatically.
For more information, please refer to:
http://msdn.microsoft.com/en-us/magazine/cc163562.aspx#S6
http://blogs.msdn.com/trobbins/archive/2007/08/31/importing-an-excel-spreadsheet-using-infopath-2007-simple-example.aspx
Hope this helps.
Lu Zou