The Salesforce Certified Administrator Certification is the entry-level certification for Salesforce administrators. I started this site with my preparation notes for this exam, and passed the exam on 11/5/08.
I would recommend reading the entire official study guide, and analyzing each bullet point for the exam. This is essentially the same strategy I took when preparing the for the exam, and found no surprises in the exam room. You can find all of my notes by bullet point in the Study Guide or all posts together in the category Certified Administrator.