Like with most things in life you need to start with the basics! You need to give yourself a good grounding in basic computer and network functionality before you attempt to tackle more specialised subjects. Even if you do have experience working in an IT environment it is still a good idea to start with the entry level exams as you will get experience with the exam styles and requirements.
In light of the above comment the best way to start your path to IT certification is with the following Exams:
The A+ exam will give you a good knowledge of general pc hardware troubleshooting and a background in how computers function. It is vendor neutral so makes a good starting point for moving into other more vendor specific certification streams.
The network plus is like the A+ exam but aimed at networking subjects, again it is vendor neutral so does not focus on specific products or technologies. It will however introduce you to TCP/IP and other networking concepts which you will need to know about during your career in IT.
The Microsoft certified desktop support technician exam is specific to support Microsoft Windows XP. At the moment this is the most common desktop operating system so learning how to support it properly will set you up for entry level desktop support roles.
These three exams will give you a good foundation to build on and are a good starting point before working on to more advanced certifications such as the MCSE and CCNA.