I have an Acer with a IDE hard drive and dvd RW master with a Sata hard drive and dvd RW slave. I just changed my IDE hard drive master with a larger IDE hard drive but I can't install XP Pro because its asking me for the O.E.M. When I first insalled the smaller IDE I wasn't asked, now with the larger IDE I'm asked. So I'm asking what to do.

At what stage is it asking for this OEM ?

As soon as I hit f6 to let xp I'm using asata device

At what stage is it asking for this OEM ?

As soon as I hit f6 to let xp I'm using asata device
Helpful Inaccurate?

That would mean it wants the drivers for the new SATA drive.
Try it without attempting to install these drivers..