XP x64 won't install

[unicorn]

Hello guys,
long time no seen! I have been busy taking pictures and fiddling inPhotoshop and get everything to work with printers, custom color profiles and stuff.

Here:

I have 4GB of RAM. XP doesn't utilize all of the memory, so I thought it was time to give XP x64 a run. It won't install. Why is this?

Booting from the CD of course, it runs and copies the usual first set of files to the HDD. Then there is a message: "Setup is starting Windows" (or something very similar) at the bottom of the screen. I sit there waiting for like five minutes, nothing happens and the computer doesn't response to keyboard hammering. Ctrl-Alt-Del - where are you when I need you?

What am I doing wrong?
Hardware should be ok, I think, ASUS A8N-Sli Premium with an AMD 64 3700+ processor. I see nothing in BIOS that should be ticked for x64. Any pointers are highly appreciated!

all the best,