First boot free Partition Wizard
bootable CD, rightclick on Windows 7 partition to Modify>Set to Active, click OK.
Next rightclick on Vista partition, select Modify>Set to Inactive, OK. Do the same for E if it is a data partition as only OS partition should be marked Active.
Next click on Windows 7 HD again to highlight it, from Disk tab select Rebuild MBR, OK, Apply all steps, reboot.
If Windows 7 starts on its own then you don't need to run Startup Repair 3 Separate Times
from the Windows 7 DVD or Repair CD, which writes the System boot files to Active partition. Rebuild MBR will sometimes suffice by itself - if not run Repairs until it starts at reboot.
Once Windows 7 starts on its own, save a backup image externally. We have never had a failure with PW CD in hundreds of these operations we've helped with here but back up still needs to be done now that Vista won't tag along. Backup Complete Computer - Create an Image Backup
Next boot PW CD, rightclick on Vista partition to Delete, OK. Then rightclick Windows 7 partition to select Resize, drag left grey border all the way to the left over the deleted Unallocated Space, OK, Apply all steps.
If resizing causes Windows 7 to fail to boot, run Startup Repair until it starts again.