Avoid reinstalling XP and all programs/files

Imagine the following scenario:

Two Hard Disk Drives in the same machine.

First drive, XP SP3 installed. Several programs installed, plus personal files. Several directories such as C:\Windows\system32, etc.

Second drive, Vista installed. But not using any dual boot setting. Both were installed, but isolated from each other. While XP was being installed, the 2nd HDD was unplugged from the hardware. Same for Vista. So you have two Op. Systems, not related with each other. And you can change the boot order in the BIOS setup.

When you start XP, you can read the Vista drive, cause it's the slave drive. Same for Vista.

Now imagine that I wish to do a complete format in the XP drive.

Then, I enter the Vista drive (or XP) and before I do the full format, I use any kind of program to copy ALL FILES from the other drive.

Really, all the files, the entire drive, even if it's 30 GB of size. Not a single file missing. Including directories like C:\Windows\system32, C:\Program Files, and all that stuff.

After the XP disc is erased, I am placing all the files in the same place again, where they were located before. And I am doing that while Vista is running. A simple copy-paste to that empty drive.

Then I reboot my machine. Will both systems work like before, or not?

I was really thinking about this, cause I wish to avoid reinstalling Windows and all programs. But I have no idea if it's remotely possible.

I know it's the same machine, same hardware, same everything.