Did you see the photos for the HD-DVD addon? It looks like there's 2 USB ports and 1 HDMI port on the back.
http://ve3d.ign.com/articles/706/706982p1.html
No word if it's the latest HDMI spec though.
The two machines do have significant differences. The $599 model offers a 60 GB hard drive. The $499 model has only a 20 GB hard drive and also lacks wi-fi capabilities, a memory card reader and an HDMI output for newer high definition televisions.
"We felt that if you want to save something...
Any wireless bridge aka "game adapter" would work just as well. It's cheaper and plugs into ethernet port. Don't get confused and buy a usb adapter (which won't work). The only working USB wireless adapter is the official Microsoft one.
Here's a $20 AR router w/ bridge functionality...