order posts from multiple blogs by date

Hello.

I have several wordpress blogs installed on different subdomains on the same domain. Each one is a different wordpress install and I do not want to change this at this moment, even the new 3.0 offer the network option. The main domain is also a wordpress, with its own posts, but I would like to show on the main page the lasts posts from all blogs, chronologically. Is there a way to read them from the database and order them by the time of publishing?

To be more exact: I want to read posts form blog1_posts, blog2_posts, blog3_posts (all using a single database) and show them chronologically. How can I do that? 10x.