I passed on my previous laptop, purchased from Dell in Jan 2003 to Binoette 1, who now wishes to sell it and upgrade to my current Dell. (hey, what are fathers for?

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Now she tells me she doesn't have the Windows XP reinstallation disk that came with it. I never used it and would have had no reason to take it out of the pocket when I owned it, and a search so far has failed to turn it up. I can't really offer the laptop for sale without it, so it's over to Prooners.
What options do I have? Will Dell give me a replacement (they will still have my purchase details)? Is it possible to buy another OEM disc, or can XP only be used on the computer it's shipped with?
Any advice appreciated before I ring Dell (since B1 also denies ever having the original sales invoice)?
Edit! Hang on, what am I talking about? My current lappy is Dell, the previous one was Acer! Sheesh.