If you want to do a hardcore Google hacks, you should look into Google API (http://www.google.com/apis/). I'm not sure though if they decided to disclose the PageRank query - last time I checked it wasn't part of API.
The checksum formula was fairly recently publicly cracked. That is how you see sites now showing the pagerank of sites without the toolbar. If you look hard enough, you can find quite a few people selling the code to do it. I would highly advise against purchasing it for several reasons, one being it's illegal to use, two being your likely to get scammed with junk code, and three Google is probably fixing to change the formula as we speak as they have done in the past.
How to make Google page rank query with PHP coding?
Linear Mode
