I am working towards my XML Certification as well. Here is some information to overflow your 'input stack'.
Links:
http://javaranch.com/gramps/XMLLinks.jsp (Tons of links)
Books:
If memory serves me, Ajith used "XML Bible" to study for the exam. In addition he recommended reading the DOM spec from
http://www.w3.org/DOM/ Additionally why not check out this week's give away book, "Professional
Java XML". Ajith rated it 10/10 as 'The most comprehensive XML guide I have ever read'. I am unaware of any specific 'Study guide for the IBM XML Certification exam' type book. Maybe someone can write one...
Hope this helps.
Glen Jansen
Java/XML Cert in Training.