<fx: Ian whistles quietly to himself about how someone was going on about how cheap and easy it was to build his own PC
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Now down to help.
In Bios, make sure you have set everything to defaults to start with. Then look for any settings about enabling SATA(Your M/board manual should tell you about this if it needs to be done or will explicitly say that it supports SATA out teh box.
Then, making sure that teh first boot device is set to CDROM boot the PC with the XP install disk in. It should start teh setup process(At this point it doesn't even know there is a HD present.) Again in your M/board manual look for any mention of a 3rd party driver disk that should be used to install an OS. If there is make sure you have it available and go through the process to install them during XPs setup.(sit and watch EVERY screen, don't try and watch TV at the same time, this needs 100% attention) It may prompt you to format the partitions that are already there. I would recommend doing this so you know that there is no 'hangover' from your previous attempt.
Let us know if you get any further