combine two databases into one?

I used to have a blog set up on a domain that I let grow dormant. I stopped blogging at that domain. But then I started a new blog a few months later. I now wonder if I could import the old posts and all into my new blog (that is over a year old by now) and it not mess anything up.

Basically, can I add the old blog to my archives.

Oh, and it was an older version of WP too. So would I have to create a new install, import and upgrade, then import into my current blog?