First you must install Windows XP and then only you can enable SATA mode as AHCI.
You can easily<a href=”http://www.techyv.com/questions/how-install-windows-xp-0″> install Windows XP</a>. After installation please follow below steps correctly,
1. You can download AHCI_Intel_v188.8.131.527_XP.zip from Acer Website.
2. Extract files from AHCI_Intel_v184.108.40.2067_XP.zip to C:\AHCI_Intel_v7_5_0_1017_XP
3. Go to device Manager, you can see Intel 82801HEM/HBM SATA AHCI Storage Controller under IDE ATA/ATAPI controllers.
4. Here right-Click and then select Update Driver. Say no for connect to Windows Update to search. Click Next.
Select install fro a list or specific location. Click Next.
Select “Don’t search. I will choose the driver to install”. Click Next.
Select Have Disk. Browse to C:\AHCI_Intel_v7_5_0_1017_XP and highlight the iastor.inf file. Click Open. Select Okay.
Now you should have a list of controllers, for the Acer 5315-2153 choose Intel 82801HEM/HBM SATA AHCI Storage Controller. Click Next.
You can see this line “Installing the device driver is not recommended”. Click yes to continue installing
Click Finish. Click Yes to restart your computer
5. When your computer boots up, press F2 to enter the BIOS. Change SATA mode to AHCI, save changes and exit.
Now your computer will find the new hardware. Wait few minutes for popup message to restart your computer. When message comes, say yes to restart your PC.