XPath Against OpenXML and OpenOffice Spreadsheets?

All I need to do is retrieve the string value of every cell of column
"A" whose string length is greater than 20 characters in length.

Anyone know how to use XPath to retrieve this from an Excel 2007 file?
 What about getting these values from OpenOffice.org's CALC
spreadsheet via XPath?

Regarding the OpenXML - I've been all over MSDN and it appears to
require an understanding of .rels files and convoluted mappings
between different sub-files???  I know I can use ADO and Microsoft's
Jet Provider to read from an Excel file (and just about anything else)
but I thought that using pure XML technologies would be much cooler.

Is XQuery a better fit for this task?

Even a hint of where to go and look would be appreciated.

- Ronnie