Broken filesystem on Windows XP / 7 virtual machine

I created a virtual machine with Windows XP as the guest system in Microsoft's Virtual PC that ships along with Windows 7.

I then installed Virtualbox and began running the MS machine in it. It worked fine.

Then, I accidentally started the machine in Microsoft's Virtual PC again. The screen stayed blank, so after a while, realizing my mistake, I closed the Machine.

Since then, the VM won't start any more, claiming massive file system problems. Starting Windows in normal mode results in a SOMETHING_FILESYSTEM blue screen; I can start in protected mode and run a checkdisk. That will fix something on every run, but every time I restart, it will start again.

I tried re-booting the VM with the Windows CD and doing a repair install. I didn't watch whether that worked out, but I'm caught in the reset / check disk / reset cycle again.

Is there anything VM specific that can still be done? On a physical machine, I would say reformat.

Is there any way to get hold of the data on the virtual machine through either Virtual PC or Virtualbox? It was an experimental machine, but I had started entering some data on it that would be nice to recover.