auto post listeners

I just read the few recommended bullet points and am trying to slim down my them in my blog, instead of writing everything about everything, but I am very much varying between flash coding, politics and personal rants, so here is what I would like to do.

Have an individual blog for every theme (coding, politics, etc.), but have one super blog that shows ALL posts from all ‘sub’ blogs.

So people could subscribe to the flash posts only, etc..

How would i be able to do that? Or is there a way of setting this up in a single blog?