Pay attention with VirtualBox 2.2.0 I found a number of problems and I was afraid not to be able to recover my VMs.
I updated my SL box and VirtualBox was updated too to 2.2.0.
When starting the VirtualBox GUI it notified the need for updating configuration files, after that it HANGED.
There was no way to wave it running with the old configuration.
Manually renaming my .VirtualBox folder I was able to run VirtualBox GUI as a new installation.
Then I was not able to import or open the existing virtual machines.
So I created them from scretch using the exiisting .vdi (disks) files.
The (Window$) VM were starting but all CRASHING at the beginning of the boot process with a typical WIN BLUE SCREEN and then looping back to boot (asking for normally or maintenance mode), none of the modes was good and the VM was looping again and again: blue screen-boot-blue screen-boot...
I also tried booting from CDROM and performing CHKDSK /F (as suggested by NT loader) but that failed too.
The solution was:
In VirtuaBox GUI -> Details tab -> General VM setttings -> Advanced tab: select IDE controller type as PIIX3
That cured the problem and VMs boot as usual.