@kael

Nevermind about vmware, I just used it to test, and it does go further than on the real hardware.

I have a spare harddisk and am trying to install on that. I just tried again and it is indeed something with EFI
"Loading /Library/System/Extensions.mkext", then a message with something about EFI flashes up for the part of a second, and the box reboots. So exactly the same problem as you guys with your semprons, but quite different specs.

specs again:
Athlon64 X2 5600+
Gigabyte GA-MA69G-S3H (ATI SB600)
2GB RAM
GF 7200GS PCI-E

Harddisk for OSX will be a 40GB IDE drive on an IDE controller (That one had a FreeBSD 7.0 with / on ZFS till yesterday.. currently unformatted)
DVD-drive is IDE too.

PS: I do not have that NX/DX options in my BIOS.