Did it help? If yes - maybe you can help me?
Yesterday Tom Lane committed enormous patch, which had commit log:
Support window functions a la SQL:2008.
Hitoshi Harada, with some kibitzing from Heikki and Tom.
… and that would be all. I will write more about it, its use cases, and some detailed examples but now I'm on vacation, and will stay here for some time. You can expect to get the post mid next-week.