The simple part is that I want to replace my hard disk with a new one. BUT when I've done that, can I happily reinstall my Windows XP Home edition OEM on the new disk with the CD? Or will the disk think that I'm trying to put iit onto another computer and block me???

Well, it probably will think you are trying to put it onto a new computer depending on which way you do it, but that problem is easily rectified by calling msoft and asking there customer support about it.

If its an OEM CD from Dell, for example, it will only check to see if you have a Dell motherboard... If you do, then the install should go alright... If not, I would do what mattofak said!

yeah, it should work, the only problem would be if it's been activated too many times.

Then you'll have to call microsoft for a manual activation.

Takes about 15 minutes on the phone, and you have to read a lot of letters and numbers in to the operator

but anytime I've had to do this, the operators were very nice :-)