The WinXP exclusive thing is bullshit, but mirrors were available immediately. What's really a pain in the ass is how servers running these maps will not auto-download for people without them. Something about how they're flagged as "official" or whatever.
Anyway, great maps. Aridoom has a cool post apocalyptic Road Warrior feel. It's especially fun with the Vehicle Invasion mutator, defending a desert outpost from an army of creatures Starship Troopers style.