copying posts from 1 install to another

I have 2 different installs of wp on same site:

1) mysite.com
and
2) mysites.com/blog

i want to create a category called ‘blog’ on main install at mysite.com.

then i want to copy all categories and posts from mysite.com/blog into the other install.

2 questions:

1) how do i do this?
2) it appears to me all urls should remain the same if it worked – is that correct?

thanks in advance for your help.