I dont think so. A lot of important topics especially those related to implementation are not included in the certification and hence it is not the best way to learn XML technology. For instance, parsers are not given a lot of importance in the objectives of the exam on the other hand
parsing is dealt with to a certain extent.
Ability to user different XML parsers and to understand subtle differences between them is a very important qualification of an XML developer and unfortunately the certification will not help you acquire this competence.
I suggest you to learn XML first, take one aspect of the technology at a time - XML, XSL, XSLT, parsing using DOM, parsing using SAX and using various different parsers. When you're feel comfortable you can take the test.
Good luck,
------------------
Ajith Kallambella M. Sun Certified Programmer for the Java�2 Platform.
IBM Certified Developer - XML and Related Technologies, V1.