That won't work. You CAN"T change OS drive letter while you are in windows. Now YES there are a few ways that require some skill to change the drive letter but from what I have seen its a 50/50 chance of it working or just having to reinstall.
Your better of just reinstalling. Backup all your files and wipe it out. THIS TIME THOUGH!!! Unplug ALL devices but the hard drive you wish to install to, Any USB Card Readers, Zip drives, USB Thumb drives ect. CD/DVD rom drives are fine. ALSO! when you go to customize the install and for the partition it will show you drive letters that are currently there. Windows 7 is pretty good about making the OS drive the C drive UNLESS there is another Formatted Drive in there (Mainly Zip Disk) that it...