What you are asking about is a master details page set.
in your master list, the list of all blogs from all categories, you would have a link that passes the blog id to the detail page.
on the detail page, the recordset would use the ID URL variable in the where clause. the database starter kit tutorial here:
http://www.webassist.com/community/tutorials/view_tutorial.php?tid=104
has an example of how to create a master detail page set.