I fixed the problem thanks to soemone on the community board. Turns out it is Bios 0117. It has problems working with 64 bit OS with 8 gigs.
Yeah Intel's BIOSs are idiotic. Right now I'm facing a problem whereby Win XP will not run setup from a CDROM, it seems to be an issue across several DG35ECs that I have. In my case even the latest BIOS doesn't fix this.
As for your problem, the DG965SSCK had a similar issue with > 3GB of RAM, the solution was to use a particular (old) version of the BIOS. Issues like these will play a serious role in my purchasing decisions for Intel hardware in the future. Sure their products are rock-solid, but their buggy BIOSes make them nearly unusable....
XP is prior to ahci. Check bios setting (ahci or ide), or f6 in the driver from the MBcd via floppy at start setup