Best option is to have the person save the file as iWork '08 before sending it to you.
Another option is to download the trial of iWork '09. If you decide to buy it, fine, otherwise when the trial expires it will become a "viewer." If you do go this route & don't decide to buy '09, make sure you save any files you create with '09 as '08 before the trial expires.
A third option is to access the PDF hidden in the Pages file package. Right-click on the file & show package contents. If this is not an option, change the extension on the file from .pages to .zip & unzip the file. Hopefully, there will be a PDF of the file in the QuickLook folder.