Andrew Park showcases a few new Media Center 2005 PCs including the Alienware DHS and HP Digital Entertainment Center, noting

”...only Microsoft has delivered true integration of computing and video entertainment.“

You can read the whole article here.  One thing to note, the HP Digital Entertainment Center currently available at HPShopping.com is the z540 (single tuner).  The z545 Andrew previewed will be released soon from what I understand (sorry, not date available).