A quick fdisk operation will get you to the same point as not having the OS installed from the factory. Plus, you can have some assurance that the computer is working correctly if you power it up with Win XP pre-installed. Just order it with Win XP and you're good to go.
Well, if you would really prefer to not have it installed, I believe you can ask them and they'll take care of it. I know PCTorque has been asked this question and they had it arranged. But, as was stated, it's pretty easy to get to the point of not having the OS installed, lol, just format the hard drive and you're good as new :-)
Yeah, a quick format will certainly accomplish the same thing really fast... Personally, though, I always do a full format to make sure the file system is completely in tact. :-) I'm pretty picky with my computer, though. I get annoyed when a program loads when windows first loads up... lol.