Different sets of tags for different categories

First of all, i tried Codex, Support Forums and Google 🙂

I have one WordPress 2.3 install, and 2 main sections on my website called ‘Blog’ and ‘Portfolio’. They are 2 top-level categories with own subcategories and can be accessed via urls like this:

domain.com/blog/
domain.com/portfolio/

I want to have 2 separate, independent sets of tags for each category. For example, for blog i will have tags:

wordpress, plugins, themes, php, xhtml, css etc

And for portfolio i will have tags:

logotype, brand book, identity, website, print, advertising etc

Each root category should display a tag cloud with only relevant, category dependent tags.

Is there any way to implement this or i should use different WordPress installations and manage 2 separate blogs?

Thanx for any ideas.