the media direct os is on a seperate partition on the hard drive, invisible to windows - at least it was on my 3 year old inspiron 640m.
if you don't ever use it, i would suggest getting rid of it to avoid this happening again in the future. i wiped mine by using a linux liveCD and using gparted. this has the added benefit of reclaiming some hard drive space - i forget how much though.
note however, that it's a difficult procedure to reverse.