i have the same problem with windows 7
i think has something to do with some patch of windows 7 some update at affect purposely the partition.
i had a samsung notebook , and it saw the partition but when i tried to modified it did nt let me to add a new partition for ubuntu.
after several tries i choose to wipe off the whole hdd then i install windows 7 then right away ubuntu and it works great.
now in my personal pc i still have the same problem, but here it get worse and weird.
i boot with live cd and i choose to install it then i dont see any windows partition and it does nt let me to install it aside anythig cuz it simple does nt detect win7 now if i boot with live cd again and i choose try ubuntu then i see all my partiotion and all my folders. but when i doble click on the icon to install it and i should have the option to choose the hdd , i dont see any partition. !!!! that is super weird.
i think microsoft does nt want ppl to have other OS beside their own.