One of my PC's is very busted. I need to take out my hdd, plug it into my other PC, and copy the windows setup files on to it (so I can do a fresh install). But how? Can somebody give me instructions on how to do this please?

use an install disk. That's the only way I know how, as when you install windows, it takes a sort of snapshot of the chipset, motherboard, etc, and unless they are identical, you are going to run into problems such as windows not working. The ONLY way I've ever seen it done is to resintall windows.

Okay, I think I got it. So, I unplug the IBM hdd and plug it into my parents PC. Boot into the Windows XP disck. This should format the drive, and start copying the Windows setup files. When its done, shut off the PC, unplug the IBM hdd, and plug it back into the IBM. From here, the installation should continue smoothly. Ok, was that right?

.........."the installation should continue smoothly. Ok, was that right?"
In a word No.
When you take the IBM hdd and plug it into your parents pc and install XP this is what happens as Valis said.
Say your parents pc is a Dell, when installing XP it will identify the hardware in the Dell pc and install.
Should you install that IBM drive back into your old pc XP will halt and throw an error msg at you.
The reason is because XP is looking for the Dell hardware signature and when it finds none it will stop.
You don't actually say what is wrong with your IBM machine as a simple fixmbr could sort it all out.

Oh, sorry, I worked it out with madmonkey (hardware help--IBM NetVista SERIOUS Bootup Problem). We/he figured re-installing Windows is the only way to fix it. I just need to copy the setup files to my hdd---somehow... My parents dont have a brand name computer. I think its custom built. BTW, my CD/floppy drive are unresponsive.