Unable to open Excel 2003 files with Excel 2007

My OS is Vista and I have Office 2007 on my laptop.
I am unable to open Excel 2003 files directly by clicking on it. I do not get any error messages. The icon for opening just rolls for sometime and then fades out(meaning unable to open the file).
I then have to start Excel 2007 and click the open icon and then browse and open the Excel 2003 file I want, which is very cumbersome.
I do not face this issue in word and powerpoint where I can easily open earlier version files directly.
Please help!
Regards,
Clifford