Win xp oem activation hits me clear as mud!

I purchased a win xp home oem disk, at only just pennies short of retail
edition price, from the supplier that supplied me with items I used to build
my own system. I already have win 95 and win 98 upgrade purchases from now
dead previous pc's. So, if my motherboard fails, am I right in assuming I
am supposed to buy a new motherboard and another copy of win xp, thereby
keeping up Bill (love him to bits) Gates to the life style he has become
accustomed, just so that I can carry on using a single system that ain't
moved anywhere and is only used by the single self same person, whose fault
cannot be blamed if the motherboard decides it wants to go to motherboard
heaven?

Thanks,
David