The Windows XP CD will do it all for you..Depending whether you're using a brand new hard drive or a used hard drive that you want to repartition, reformat and install, the links below will walk you through the process. You may want to print out the various pages before beginning.:

Microsoft's Windows XP Home CLEAN Install On New Hard Drive

Microsoft's Windows XP Home Install On Old Hard Drive

If you're talking about which key to press at the very beginning of the install process, after the XP CD starts to boot and says: "Press any key to boot from CD", simply press any key.."Enter" or the "Spacebar" will do.

Hope this helps.

Grif