I have a extra sata hard drive has xp on it and the one is in my computer has win7 64 bit but I am trying to get rid of w7 cause about 80% doesn't work with it. I have try to put the xp hard drive in and put the xp disc in and gets a certain point than gives a error message won't load xp. I am not able to change anything in the BIOS changing from achi to ide cause its not listed.
The system files that are loaded in your XP installation are specific to the PC it was installed on. Generally speaking, you can't just swap an existing installation into a different computer (it doesn't contain the necessary system files to function properly). Also, unless you own a "retail" version of XP (or a non-manufacturer specific "OEM" version), then the installation is only licensed to for the PC it came with and it may be BIOS-locked to only function on that original PC.
If you own a retail copy, then your best bet is to take Thayne's advice and perform a clean XP install onto a freshly formatted hard drive. You might be able to get away with performing a repair install, but that method often results in system errors, and never works as good as a clean instal (if it works at all).
Good luck