Hello Vokerain, welcome to Seven Forums!
First things first, let's make it so you can remove Vista.
The first thing to do is mark the D: partition (Windows 7 right?) as "Active" so Windows will know where to create the new boot files needed to start Windows 7; after that you will need to run
3 separate startup repairs with a system restart
between each repair to create the files to the Windows 7 partition; it's really easier than it sounds.
All the info needed to do this is in this tutorial at the link below and be sure to post back with any further questions you may have and to keep us informed.
Startup Repair - Run 3 Separate Times