Pulling in posts from another blog

I’m trying to figure out the best way to do this, but haven’t got there yet.

I have various blogs at sites on sub-domains, so for example, entertainment.inhampshire.net, business.inhampshire.net, et and each of these will have posts specifically for them.

However, what I’d like to do is have the main site show all the posts from these sites. What would be even better, would be to have them all linked to one database, and I can then select what post goes where simply by the category that it is added to.

I tried to do the latter, but only got all the info from a single blog (the first one to use the db), such as the header, footer, etc.

Is there a way to do this?