Installing Windows 7 with xp

Hi, well since the RC is going to go down on the 20th I decided to download Windows 7 and now I want to install but I want to keep my XP partition intact. I've been looking online and people say to resize my Windows partition or something like that but when I go to disc utility it won't let me do that.

So can someone point me in the right direction or help me with this, I just want to triple boot (if it's possible) with 10.5, XP and 7.

Thanks,
ChrisN

http://lifehacker.com/5126781/how-to-dual-boot-windows-7-with-xp-or-vista

Is this what I need to do?