|Firstly you need a working cd/dvd player to be able to install XP, to install it from a folder, you would still need the cd player to be able to copy the files onto the hard drive folder.|
To setup from a folder a XP floppy boot disk would be needed.
Secondly if your computer has a sata hard drive you will need drivers from Acer for it as well as all other XP drivers it requires.
Next you will need to create a partition for XP on the Vista drive unless you already have it partitioned, or you have 2 hard drives.
If you get this far you will need to use a partition manager to enable you to boot, both Vista and XP.
Installing XP after Vista will destroy the Vista boot loader.