First-level directories for categories

I would like categories on my site to be found at http://example.com/whatever/ rather than http://example.com/category/whatever/

I presume the reason that this is disallowed is because going to http://example.com/wp-admin/ would attempt to list the blank category wp-admin rather than the admin panel.

Is there any workaround to make this possible, or indeed is it possible using only WordPress?

(I’m using v1.5)

Thanks!