Got this off another dlist I belong too.  I tried it with Ringo's microchip and it worked, so I thought I would share it with you guys.  Might someday come in handy.

A site where you can look up any chip number
petmicrochiplookup.org/

The results are returned with the most recent entry displaying first. Therefore, start by calling the company listed first in the "enrolled with" box. If you are unable to get the correct information from the top record, work your way down the list. Please be advised that this tool is a beta-version and is still a work in progress.The site was launched last month ; three of the six major registries in the United States are working with the organization, and additional participation is expected soon.

A site for international registries can be found at
http://www.petmaxx.com/start.asp