if you have problem with installing xp, please do this.
Disable the native-SATA in the BIOS
If the BIOS provides an option to disable the native-SATA configuration in the BIOS, do the following steps.
1. Turn off the computer.
2 Press the power button and press f10 to open the BIOS Setup.
3. Use the cursor to navigate the Configuration options to locate the Native-SATA setting.
If there is a SATA setting, select the Disable option, and then press F10 to save the change and restart the computer.
If there is no SATA setting, use one of the other options in this document to change the settings.
I had the same problem with a Toshiba Satellite A300D, I could not find drivers for Sata. But when I looked into the bios menu, I saw an option like this: "Sata drive configuration: 1.AHCI and 2.Compatibility. I've select compatibility and I managed to install windows xp.
Acer Extensa 5220 same problem with SATA.
Dowloaded the drivers SATA from Acer.
Copied to USB , files in/out original folder .
Inserted while I was installing the XP .
Did the F6 gig,didn't worked.
Restarted the whole process with usb inserted and .... MIRACLE !!!
My HDD was there.
Good luck :)
Remember you not upgrading, you doing downgrading. an order to intall xp over vista, you need to erase everything in the system. erase every data in the hard drive. there is a boot cd for that. the boot cd will clean everything and aloud to install xp.