|Do you have an XP Install CD?|
What type of hard disk do you have? IDE or SATA?
Do you have your XP Key written down?
Do you really have only 256mb RAM in a dualcore system? I somehow doubt it. or is it your graphics card that has 256mb of ram, and your system has 1gb or more?
What happened to your old hard drive? Was the operating system on it still serviceable? Do you want to clone the old drive or do a fresh clean install?
Do you have your motherboard driver disk? Do you have driver disks for other things such as the graphics card?
If the new drive is SATA do you have the SATA driver available on a CD or floppy?
Have you seen the menu to the right? There is a link to How-Tos.
Go there and scroll down the list and you will find one that says "How to install Windows XP"
I'm not going to re-invent the wheel for you.
Goin' Fishin' (Some day)