installing winxp pro SP1 on a pirate cd key

hello!

while moving house, things tend to go missing (or most likey thrown out by mistake), and one of the things that went missing this time was my cd case (and cd key) for my winxp pro...lucky the cd was in my cd holder type thing, but unlucky in the fact that i have now formatted, used a pirated cd key (cause im not going to buy another bloody copy of the thing) and now cant install the sp1..

My question to you all is, what is the way you can get around this protection of sp1....ive heard you can do it, but right now im at a loss......