As an entry-level (or at most, a just-barely-mid-level) certification, the CCDA aims to identify individuals who know how to design relatively modest networks around Cisco systems and components. If you do some poking around at a few Web sites -- most notably, http://www.gocertify.com, http://www.itcertinfo.com, and http://www.certcities.com -- you should be able to learn plenty about the CCDA and other certifications that might interest you. The recommended course of study to obtain a CCDA is to first obtain the CCNA. If you're starting from scratch, I'd precede that with the CompTIA Network+ and i-Net+ certifications as well.
I hope this answers your questions, or at least lets you know where to go looking for more answers. Good luck with your program of study.
This was first published in October 2002