First, instead of 488 you should look at 158. IBM is withdrawing 488 (I believe at the end of June, from the top of my head).
Second, I was able to prep for 488 (and these same resources should work for 158) by using:
(Available from java.sun.com)
1) The EJB 1.1 Spec
2) The JSP 1.1 Spec
3) The J2EE 1.2 Spec
(Available from www.ibm.com/redbooks)
4) The WAS 4.0 Handbook
5) The WAS 4.0 Developer's Guide
Take a look at www.ibm.com/certify
and examine the recommended educational resources. Also take the practice test.
I basically blew off the VAJ portions of 488 since I knew I would be taking 157/158 in the future. I was able to pass 488 just fine without worrying about VAJ.