How do I stop 2003 spreadsheets automatically opening in Excel 2007??

I currently run a Win 2003 server with Office 2003 installed.i have recently
installed Office 2007 .
I need spreadsheets created in Excel 2003 to be opened (by default) with
Excel 2003.
At the moment if I double click on a spreadsheet ANY spreasheet Excel 2007
opens it.

I have tried changing the file association using the administrators login
however this did not work.