I got burnt by this one – all Java processes spin at 100 CPU on update 4.0.6 of VirtualBox.
A work-around is to go to Control Panel / System / Advanced / Environment Variables / System Variables and add a variable called “J2D_D3D” with the value “false”. This will supposedly disable Direct3D in Java.
via #8794 latest update breaks Java on XP guest – VirtualBox.
Simon Major’s Blog 
Thank you!!
This issue *still* persists (and is actually worse, if that is even possible) with the latest and greatest of everything (Vbox 4.0.8 and JRE Version 6 Update 25).
How they manage to introduce yet more regressions into a supposedly regression-fixing bugfix update I have no idea.
I could not even *launch* the Java control-panel applet before I found this fix!
The other alternative would be to remove DirectX (in Safe Mode) from Vbox Guest Additions, which I don’t like.
VBox Host: Windows 7 x64 SP1
VBox Guest: Windows XP x86 SP3