Triple Boot possible?

Ok, I run WindowsXP Pro all day long, I was thinking about going to Windows64bit to give it a try and whatnot. I also want to run Windows 2000. Is it possible to triple boot?
Windows XP Pro
Windows XP 64Bit
Windows 2000

Very possible. I've had as many as 5 OS' on a single system. I've never tried three Windows operating systems at the same time though. The five were XP Pro, 98se, Fedora, Mandrake, Redhat. I did however use LILO Or GRUB (boot loader, I can't remember which), for OS boot selection. There was a kid that did a project and had over 30 OS' on a single system. The only unknown in your case would be XP 64-bit. But, I don't think it would make too much of a difference.

Thanks - I just want to try Windows 64bit, see if there is really a differnce, and Windows 2000 I want to see how high I can get my score in 3DMark 01

Like I said earlier your only issue will be installing 2k after xp. xp64 might react the same way. My advice would be install 2k then xp then xp-64. However since you have xp already installed I say go for it and we'll troubleshoot from there. Moste we will have to do is modify the boot ini file.