Cloning system drive

[stevenrw]

I've just had to replace my system hard disc as it was starting to show signs of failing. I took the opportunity to upgrade to Windows 7 Professional (32 bit).
Now, here's the thing. I chose a Western Digital 1Tb Green drive believing (foolishly) that since I'm not a gamer I would not notice much difference on speed due to the 5400 spin speed. I have been proved to be wrong on that score, no matter what you may read in the reviews, there is a noticable drop in performance when saving stuff, backing up, copying etc.
So, another Caviar Black 7200 drive will be going in.
My question is this. I plan to clone the 5400 drive which contains the os across to the new 7200 drive and make that the system drive. I'll be using the free Acronis WD edition to do this
So I have the 5400 drive which is designated "C" and the new 7200 drive, containing identical files, that I want to make the new system drive.
So I need to make the new one "C" and the previous drive "C" to be some other drive letter.
My question is this. Obviously I have to redesignate the old system drive first, say drive letter "X" before I can change the new one to letter "C". Can I change the drive letter of a drive whilst it is still effectively running the system? Indeed, will this cloning operation actually do what I'm expecting of it?
All assistance from you clever lot will be greatly appreciated.

[kinmel]

Have just the 2 drives connected and leave the original drive as "C" then run the cloning software.  After the cloning has finished,shut down, remove the original drive and swap the cable over from the old drive to the clone, this keeps the hardware paths as they were for the original "C" drive.

On re-boot, the clone is now "C"

[Lance]

I think that is the key - to use the supplied (or downloadable) disk cloning software.

[stevenrw]

Thanks guys, I'll give that a shot. Problem is, as Glenn pointed out here, absolutely accurately
http://www.idnetters.co.uk/forums/index.php/topic,27330.0.html
Drive prices, having been dropping for so long, are now going through the roof, due to the floods in Thailand.
I guess we've all been spoiled in the past.