Hi,

I have the registration key for windows XP but have lost the installation disk, can I use a different copy of XP with the key to reinstall XP?

Appreciate any advice

Negative. If you can't find back your CD that Key is no use on another CD. Each CD has a unique code.

r4romay not entirely true.
If it's a restore CD then possibly, but if the key is legit then it will work with any XP CD.
The key isn't written on the CD installer anywhere, it is varified by Micro$oft when you activate XP.

Right. If your key is from Microsoft and not a special OEM license, then you should be OK using any Microsoft XP CD (not another OEM version).

haha, yes you can. The code has to be for the same type of windows xp which there are a couple. Just make sure you have the same key. There are even programs that run a random seed that will produce perfectly working keys.