Hi
Firstly;
"The device driver for the 'Intel(R), Wireless WiFi Link 5100' device is preventing the machine from entering standby. Please close all applications and try again. If the problem persists, you may need to update this driver."
This is Wlan card and it seems that WLan prevents the notebook to go into standby mode.
So as suggested in the message, I would recommend updating the WLan driver firstly to get this working again.
Secondly;
Regarding the AHCI/SATA driver;
I recommend creating new Win XP CD which would contains the SATA drivers.
Then you can set the BIOS SATA mode to AHCI and could install Windows XP using the new disk.
Here is a nice description and instruction how to do this:
How to integrate a SATA AHCI driver in a Windows XP Setup CD
http://aps2.toshiba-tro.de/kb0/TSB85017Z0000R01.htm