Okay. I've got the solution.
I've checked the running processes list while trying to run VMLite and found something like camera.exe (it wasn't the exact name). It was part of a driver
for my cheap webcam I've used with my Vista before. The driver wasn't compatible with 64-bit Windows 7 (even though the manufacturer claimed so in e-mails), but I failed to remove it after finding this out. After finding this process I've purged everything related to the webcam remaining on my computer as this was the only thing not working on my computer apart from Virtual Machines.
And now both Windows XP Mode and VMLite starts, and I hope I will have no further problems.
So after all it was some kind of a driver crash, even though I can't really understand the connection. I'm sorry huisinro that I've led you down the false trail, I wasn't aware of this problem until minutes ago. I'm nonetheless thankful for your efforts.