You must use a full retail or OEM version of XP (not the cd from your old computer) this makes life really easy and can usually be downloaded from the web.
You must also have a genuine XP key, which has not been used on another system (without genuine key you will not get updates and your system will be labeled as using pirated software by Microsoft.
Next you should know or find out the specifications of your system, to do this goto Manufactures website.
The most important step is to find out if your hardisk is using SATA interface (if so you will require the SATA XP drivers and a floppy disk, as this is the only way that XP can install these drivers.)
Install XP via cd rom by booting cdrom at system start (if you cannot do this then you must access your system bios at first boot by pressing F2 or Del keys(or whatever key your system uses) and change the boot option to cdrom as first drive.
If your system uses SATA press F6 when XP prompts “press F6 to install other” at very beginng of XP install and install sata drivers from floppy.
Use our guides to install XP
After install you will have to install your systems other drivers(ie. chipset graphics audio etc) found by reading your system specifications and downloading from your Manufactures website)
AN XP INSTALL IS NOT FOR THE FAINT HEARTED AND WILL REQUIRE A THOROUGH UNDERSTANDING OF YOUR SYSTEM SPECIFICATIONS A FULL RETAIL OR OEM XP DISK AND CORRECT XP DRIVERS.