Vista Upgrade due to Computer Upgrade

[Cuperdon]

I am planning to do a major renovation with my computer.
I'll be doing these changes:

VIA motherboard to ASUS P5Q-PRO
2 DDR 512MB RAM to 2 DDR2 1024MB RAM
Intel P4 2.4Ghz to Intel Core Duo 3.0Ghz
AGP Graphic Card to PCI-E

added on with an extra fan and a change in Power Supply.

Because of the XP (Professional) OEM license restriction, I will have to purchase a Vista Ultimate Upgrade.
I need to know when is the right time to do the upgrade. Should I do it before or after the hardware upgrade?
Because I heard that in order for the upgrade to work, I have to have a working and activated operating system before.

So after I do an hardware upgrade, should I reinstall XP anyways and get the reactivation notification and then upgrade Vista, or just upgrade to Vista right ahead?
Or should I just upgrade now and reactivate again after the hardware upgrade.

I will back up my important files, but please don't ask me wipe out the XP partition and do a clean install. It would take too much of my time to recover the programs I wanted.

All your help is appreciated. I thank you in advance!

[lostcoast]

I would do the upgrade, see if xp needs reactivation or not and then add vista, if I did it your way.

it is best to have your personal files off the computer on an external drive at all times.  I would suggest a clean install of vista on a new drive and dual boot option be in place, think about it...the xp just as it is with no risk of upgrade and vista all clean and ready to rock without a ton of old xp system files left behind to slow it down and tons of extra drive space.

upgrade versions do clean installs just keep the xp disc handy because vista will ask for it for a few sec's.