x201 came with pre-installed windows 7. There is also a recovery partition and system_drv.
I resized the windows partition from windows. got 74 gb (out of 320)
There was no problem installing ubuntu from a cd (ubuntu 10.04). windows did some check before starting and then everything worked.
if i’ll have time i might also put mac os x on it. but there is really no reason since it doesn’t support tablets, underperformed comparing to ubuntu when doing c++ calculations.