"I was told that ALL of their new systems come with Vista."
Nope. You are probably looking only at the low end products they have. I only buy their high end products which are designed for commercial use and not home users. If you go to their web page you can find models that give you options on what OS you want. You can also buy a box without an OS, but then you have to search for XP on your own.
I bought a copy of XP Home with SP-2 for $99 from NewEgg. The sale is good until March 15, which is when I suspect they will cut the MS XP cord.