I've used Regvac so often the vacuum hose has worn out <grin>

I now need to start (reinstall)  XP Pro (SP2) from scratch because start-up now takes up to 5 minutes... I frequently defrag, run current anti-virussruff and Adaware and Spybot.

but how to reinstallwithout having to re-download all the Microsoft updates?
If someone can point me to an answer, thanks in advance.

   I don't think that you are going to be able to reinstall without redownloading the updates.
   You could just reinstall Windows to the same directory where it is (without removing it) and it will simply correct any bad files or registry entries.  In this case, you will not have to reinstall any programs or updates, but you will also still have the problems that you had.
   The only way to get rid of all of the trash that is slowing down your system is to reformat the drive (be sure to copy all of your important files before reformatting) and install Windows.  You will also have to reinstall all of your programs and updates.  It is a real hassle which will take you many days to do.
   Another option which is probably sounding good about now is to buy a new computer.    Or just put up with the slowness.

Ray is right aside from the FACT that it's not a matter of opinion : you will NOT be able to reinstall WIndows without reinstalling ALL updates , which means downloading them , unless you use BART PE environment and a procedure known as slipstreaming SP2 ; this amounts to burn a copy of your orginal CD and use BART'sprocedure ; if your HD is not recent (less than 3years ) , you will have the possiblity to reinstall windows WITH SP2included ; other updates are not included but at least...
Tell more why you need to reinstall instead of restoring to an earlier date .