Question: I bought a new HD (1 TB) which was my D drive. I want the new HD to be C drive and someone helped me to change that. Now my new HD is C drive but with 2 OS (Windows 7 and Vista). My old HD is now D drive also with Windows 7 on it. So now I have 3 OS on my PC. How can I delete Vista on drive C and the other Win 7 on drive D.

I only want the Windows 7 on the C drive. Windows 7 Ultimate must be my main and only OS. So..... When I delete the "Windows old" directory it should work fine or do I still have to do the boot ini thing? Where do I get this bcd?

Answer: 
Boot up the machine using a Linux LiveCD, such as Ubuntu. 

Then you should be able to edit the disk partitions with `gparted` and delete one. 
You can then create a new partition in the free space, or expand one of the other ones to fill it. 

The problem with using Disk Manager through Windows, is you may find it impossible to edit the disk that's currently in use.
When you install another copy of windows on partition which already contains windows, the old one is moved to windows.old directory. All you have to do to get rid of it is deleting this directory. 

Second step is fixing your boot.ini file. The easiest way is using 3rd party software like easyBCD to remove spare entries. Be careful though - deleting wrong entries will make your PC unbootable and you'll need windows installation disk to fix it.