I am able boot Hexxeh’s Chrome OS Vanilla builds in Virtualbox but I found the mouse cursor is stuck to the middle of the window.
I was able to solve this problem by selecting “Disable mouse pointer integration” from the Machine menu in Virtualbox’s display window.
You can also toggle this option using “Host” + I, the host is the right-ctrl button by default.
This problem seems to stem from Virtualbox’s feature that maps the cursor position from the host window, with this disabled you now need to click into the Window to allow the guest to capture the mouse and resume control from where you last left the cursor, which is not as nice but hopefully this bug will be fixed someday. However, if you find a better solution to the problem please leave a comment to let us know!