selomelo - 3:01 pm on Feb 12, 2006 (gmt 0)

I tried replacing the url with my own - error=forbidden. What is this?

The number in question is unique to each page. That is to say, each and every page has its own magic number (checksum). To make the query with yourdomain, you need to know this number.
There are some free pages that offer PR prediction, etc. For example, search google for "pagerank prediction"