After having my RCP app running for a while on Windows XP 32 bit I had to deploy it on a 64 bit XP Windows using a 64 bit Java JVM.
Well, the Windows XP 64-bit machine had both the 32 bit and 64 bit Java 1.6.0_14 JRE installed, but just double clicking on my launcher always picked up the 32 bit JRE.
Now, adding the --jdkhome "C:\Program Files\Java\jre6" (Remember: there are two (2) dashes) to the 32 bit launcher executable, my RCP app launched happy in the 64 bit JVM. Using Help -> About gives this:
So a primitive solution is to add your own little ".bat" file where you add this option to the launcher.
I have not yet tried this on Nb 6.7 where some major rework was done on the launcher code.