Firstly, make sure you have a working system repair disc before changing the drives around. The Backup and Restore control panel has an option to burn a system repair disc in the left-hand pane.
Then, use bcdboot to install the boot loader:
bcdboot c:\windows /s c:
You will also need to set the partition as the active partition on the drive:
select volume c:
You might also need to use
bootsect (available on the repair disc) to install the master boot record and/or partition boot sector. This usually won't be necessary if the partition was formatted during Windows 7 setup. (Because these live in parts of the disk that are otherwise unused, they're written whether they're needed or not.)
In some situations the boot settings created by bcdboot will no longer be valid after shifting the drives around. If the system doesn't boot, use the repair disc. You can either go to a command line and run the bcdboot command again, or just let the automated repair fix the problem for you.