Windows

I have a WD 500GB portable external HDD that I used with Windows and used as regular storage. Some months back, I got Ubuntu on to my PC. I partitioned the WD external HDD to try external booting - just for fun. I may have used diskparted to partition it.
Now the problem - When I try to access both windows and ubuntu partitions from Ubuntu, I can see them fine. But Windows is unable to see either of the partitions. It asks me to format the drive.
Is there any way I can make Windows recognize it? I know there was a fdisk/mbr command in earlier Windows. Is there a similar command in Win 7? Appreciate any help in advance.
Thanks.