Multiple blog capability is planned for the future. For right now, the existing "workaround" is to install WP into separate folders for each blog. You can still use a single database, however. What you do, is give each blog a unique table prefix; this is done when you create/edit the wp-config.php file. All the blogs would point to, and use the same DB name and DB username, but the prefix would be, for example blog1_, blog1_, blog_3 which you would have specified in each wp-config.php file.
Have I made any sense with that explanation? :) If not, just post back and I or someone else will clarify for you.