A good starting point is probably to review the IBM website:
http://www-03.ibm.com/certify/tests/obj486.shtml More specifically, the recommended training resources for a self-study approach:
http://www-03.ibm.com/certify/tests/edu486.shtml i.e. UML distilled etc.
This book is probably worth reading whether or not you decide to pursue taking the examination. It's a very thin volume.
Then, there is a search link at the top of the page:
http://faq.javaranch.com/Search?search_forum=61 This should bring up dozens of earlier threads on the topic covering things that should help you get started. Use the search terms "IBM 486", "IBM OOAD" or just "486" as that is the exam number IBM uses.
Allegedly, this exam will be discontinued at the end of the year or sooner. It may or may not be replaced by an exam that covers a more up to date version of UML. The current exam covers UML1.x so that is something to bear in mind.
FYI: Passing this exam does not give you a certification. You will need to pass some other exams/modules to qualify for a relevant credential:
http://www-03.ibm.com/certify/certs/adedwssv5.shtml If you're interested in learning about the unified process etc. then there may be some value in pursuing IBM 486 as a standalone test.
Good luck!
[ March 07, 2007: Message edited by: Peter Cook ]