MacOS – Does Java come pre-installed on Mac OS X 10.7/10.8 and beyond

According to Apple's documentation:

If your Mac has a Boot Camp partition with Windows XP or Windows Vista, you can continue to use your Boot Camp partition, but you can’t upgrade to Boot Camp 4.0.

So it sounds like if you upgrade to Mountain Lion, it won't touch your Boot Camp 3.x installation; you won't get Boot Camp 4.0, but you'll be able to continue using XP.

However, I think if you do a clean install of Mountain Lion, that will install Boot Camp 4.0 by default, which requires Windows 7. So you can only keep XP if you do an upgrade, not a clean install.

You need to also copy the Contents/MacOS directory and Info.plist from the 1.7 SDK and adapt them (by changing the version strings in it).

Then you can:

$ export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home
$ java -version
openjdk version "1.8.0-ea"
$ /usr/libexec/java_home -v 1.8*
/Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home

Note that this is a hack and I didn't try anything else than start java... I was just building on your tip of creating the package.