change default program for opening word docs

Hi there,
I have Word 2008 installed on my Mac and I would like to make Pages 08 the default program for opening docx files.

I have right clicked the file, chosen open with, then selected Pages, then clicked always use this program. However when I go back to the docx file it still says that Word 2008 is the default program.

What am I doing wrong?

Thanks,
Steve.