Need help here, currently using window vista ultimate 64bit, trying to reformat by installing window xp pro sp3 cd but it wouldn't let me run the setup due to compatibility problem.

Com specs:
AMD Athlon 64 x2 dual core 4000+
Asus M2A-VM
1gb ddr2 kingston 667mhz x 2
80gb SATA seagate hdd

Currently just added my old IDE seagate 80gb from my old com using ide cables provided with the motherboard

Anyone kind enough to guide me step by step to reformat my com?