Optional packages, such as Java 3D and JAI, need to locate the system JDK and JRE in order to install into the respective ext directories.
For example,

Java 3D installer will report to install into the following location :
C:\Program Files\Java\Java3D\1.4.0_01\
C:\Program Files\Java\jre1.5.0_XX\
C:\Program Files\Java\jdk1.5.0_XX\
C:\WINDOWS\

where XX is the JDK update number.

But with JDK 5 Update 11, Java 3D installer unable to locate the JDK location.
The Java 3D installer reports to install into the following location :
C:\Program Files\Java\Java3D\1.4.0_01\
C:\Program Files\Java\jre1.5.0_XX\
1\
C:\WINDOWS\


I have verified that this problem does not exist in JDK 5 Update 10 and JDK 6 FCS.