Migrating All a User's Posts from One WP Blog to Another

Hi, I just had a quick question, does anyone know how I can migrate one of my users from one WordPress installation to another?

Say I have an author or a contributor that has been writing to blog 1 (advertising agency) and they are moving over to our blog, (blog 2) and moving all of their posts, how can we go into blog 1 and take all of his posts, including attachments, posts, preferences, etc. and move them into blog 2?

User @ Blog 1 (344 Posts, 5 Pages etc.)

I want to move him to:

User @ Blog 2

Thank you so much ahead of time for any advice.