A picture of your Disk Management window might be more helpful. Use the snipping tool and attach using the paperclip on advanced replies.
But if you installed Windows 7 after Vista, the boot system was probably set up on the Vista Partition, since it was probably active. But in any case, the boot occurs on the active partition.
Drive letters can be a little misleading. Since the OS partition is normally shown as C: , I like to refer to partition numbers. So if you installed Windows 7, was it on the second partition on the drive, and I am assuming you have a single drive system.