Java Web Start does not come with 64-bit builds of the JDK. Why is this? What is lacking that keeps it from building and working?
Thought you'd might want to know the new update is out: http://java.sun.com/javase/6/webnotes/6u12.html
64-Bit Browser Support for Java Plugin and Java Webstart This release supports the New Java Plugin and Java Webstart on AMD64 architecture, on Windows platforms. A Java offline installer (JRE and JDK) is provided. Note, if you use 32-bit and 64-bit browsers interchangeably, you will need to install both 32-bit and 64-bit JREs in order to have Java Plug-In for both browsers.