XP works very nice on E780.
Off the top of my head I'd say that this is a problem with the sata hdd. Go in to BIOS settings and go to Advanced > Internal Device Configurations and set the following settings accordingly:
Serial ATA Controller Enabled
SATA Controller Mode Opt. Enhanced
AHCI Configuration Disabled
Then save the settings and reboot the system. Now it should boot into windows and everything should work ok. So this means that if you want to use AHCI, you'll have to update the SATA hdd driver. One way is to modify the XP installation CD using nlite. The other way is to update it in Windows. Don't know why but I usually prefered the 1st option. Google is your friend and will assist you in this process if you have problems.
Hope this helps.
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