So you want to dual boot?
Why not use windows7 and wipe the disk with xp on? You could use it for music/photos or anything you want.
Unplug the old drive
Install the new drive with windows7 on,
Reconnect the old one so windows7 assigns it as drive D: and then drag to the new drive what you want to keep.
Format old drive and use for storage.
You ideally want windows on the new/much faster drive, just for a better experience.
Yes, just pull the power conector out of the old one.
Fit new drive, install windows 7, install drivers.
Reconnect old one, it may or may not give you the choice of dual boot when you restart.
Load windows7 and you will see that the old drive will be D:
Load xp and new drive will be D:
Boot into windows7 and keep what you want from the old one/format it.
I think I'm starting to get it now.
If I boot into 7, my old 160Gb drive will be seen as drive D, if I boot into XP, my new 640Gb drive will be seen as D. Correct?
Looks like an upgrade, so install fresh, and I think it asks for your xp install key during install.
Yes, with the caveat that Windows Installer has to be able to see your old version of Windows.
If you remove your old drive, the installer will not see your old version of windows, and the key you have will not work.
Then you'll have to install 7 twice. Once with no key, then a 2nd time with your upgrade key. Both clean installs. The 2nd time the installer will detect a valid OS on the drive, and your upgrade key will work.
No. Vista was the last time they asked for a previous OS key. Win7's installer is new (and different).