Thanks for the specs. I've checked out asus website but nothing obviously wrong.
The memory you have isn't on their qualified vendor list but this doesn't seem like a memory issue anyway so don't worry about that for now.
If I were you, I would reset the bios (using clear cmos jumper), if there are any bios settings which you know must be altered from defaults, then do so.
Disable any onboard features that you don't need, either by jumper or in bios, remove any add-on cards except graphics.
Remove the secondary/slave hard drive & any optical drives except the one you use to install XP with.
Disable any integrated cards as well ie. sound, lan, modem etc. I don't know if you can actually disable serial ata but if you can, then do so as you are not using it.
Try and install XP again. If you still have problems, I would try a different graphics card if you can.