How to change the system disk for a new one ?

I see drive letters are a common problem with Seven.

I did not see the solution to this:

I have dual boot with XP and Seven

The letter of these 2 partitions are:
under XP : C Sys and Y : Sysseven
under Seven : C Sysseven and X : Sys

A third partition is D Docs the same on the 2 systems

Till there everything is OK.

Now, I wanted to upgrade my Harddisk (it's on a laptop)

I made first 2 Ghosts under BartPe (external CD) of the 2 system partitions.
So I had no access to changing drive letters from there naturally.

put back the 2 ghosts (Sys and Sysseven) on a new partitionned usb drive

switched the 2 harddrives (the old one and the new one in the laptop).

When booting (either Seven or XP) I had the message I should "repaire the computer". I did it to go to Seven, thinking it would fix it. After all it was not the same boot disk any more... It's obviously a new system that tracks every little part of the system to avoid illegal copies. But I think it goes too far now...

Repaire with the Seven DVD

But it did not dispatch drive letters the right way...

So Seven said (reconstructing the Desktop because all personnal data are on the D Docs drive: "This not a valid copy of Windows" and nothing else on the desktop.

I launched Task Manager (the only thing I could do) at this step.
Launched a new task "Explorer" from there. I could see with system information that all 3 drives had false letters, but "My Computer" was not operationnal and I could not fix it. No way to access drive management...

So please tell me if you see how I should have proceeded to make it work ... !!

And how I could now fix it ?? Almost nothing works in Seven. I saw no way to tell Windows he was wrong to think my version was not authentical...

Thank you

PS I still can put back the old Harddisk but it's not the goal...

My problem is solved. I found a good message on this forum (by the admin thanks !) which explains how to change drive letters from a command prompt with the diskpart command.
It's not quite easy because you have to rename partitions in the good order and after that, once repair done, you are able to reassign letters correctly from within Seven.