I run two blogs. How can I use Seeded Buzz with both? Do I add the second blog to this account or open a separate account? Can it be done?

From what I understand, you must have a separate account for each blog. That is because each blog has to be approved before an account can be started.
If you have changed your blog's web address, for example when I finally got my own domain name, you can contact a staff member and they will see that the new url gets attached to your account.