Advice on MS Policy & Best Hardware Upgrade path for w7

[ahhaa]

I have a couple old workhorse desktops that are running XP.
It seems win7 requires full reinstallation on XP machines, and I was considering upgrading the mobo & CPU on one of them anyway. With a Vista laptop too, the Family Pack Upgrade looks like best bet.

I was wondering if it makes sense to upgrade the hardware (mobo & CPU) now under XP, so the machine would need a w7 upgrade instead of a full version.

But... what exactly is M$'s policy on XP reinstalls? Do they consider it the chip, or the board, or the OS's HD?
And would the timeframe be really short, or on into the demise of XP support?
(And, ditto this Q for Norton and any other machine-locked softwares.)

[jagabo]

But... what exactly is M$'s policy on XP reinstalls? Do they consider it the chip, or the board, or the OS's HD?

It's a combination of parts. CPU, motherboard, NIC, drives, RAM, graphics card, etc. Some number (6 I think, NIC counts as 2) can change within some period of time (6 months?) before it's considered a different computer. If your reinstall won't activate you can usually call MS and say your motherboard died and you had to replace it -- they'll usually accept that.