Want multiple blogs in one install

I want to run multiple blogs on one account. At the least, I want one password-protected private blog and one public blog. I have read that one way to do this is to have two separate WP installs – use one for private blog and one for public blog (I’d rather not do this for administrative reasons). Another option seems to be “Virtual Multiblog,” which should allow you to have multiple blogs on one WP install. If anyone can help with advice on the best way to proceed, I would appreciate it.

Also, please clarify. It seems as though within one WP installation, I can only password-protect individual posts. Is there a way to password-protect at the category level?

Many thanks,
– MA