Treat categories as sub-blogs

Hi,

I would like to partition my blog into different categories, such that each category would have the look and feel of an independent blog.

Theming of a specific category page & separate RSS feeds are already possible, however I lack the following features:
a. Display a category as a pretty url (http://myblog.com/mycat/ instead of http://myblog.com/?cat=3).
b. When initiating a search within a category, search only within the category (i.e. “remember” you are in a category). This also applies to archives, tags etc.

I haven’t found any plugin that does either of the two (b is more important). Does anyone know if such a plugin exists? If not, I am willing to try and develop it. I’d be happy to get some advice on getting started.