comcast's faq says that DOCSIS 1.1 is desired, but almost every cable modem I've ever seen for sale is listed on their compatibility list. Only the newest ones are listed as totally compatible, but almost all of them say they will work. Just the older ones are tagged as being less desirable and shouldn't be replaced with the same model if they break.
The comcast salesjerk told my wife that "they all use the same standard" and that they are forbidden from recommending any particular brand or model. It took 20 min to find their compatibility list and I just hope that the list is valid for the Dallas area.
I think I'm going to go with a dlink DCM202. I found reviews that say it works with comcast in Dallas, it's on the compatibility list, and I'll be using a d-link router so if something doesn't work then d-link tech support can't blame the other piece

The price is decent I suppose... They want either $5 or $10/month to "rent" one, but this dlink is $59.
I do have another cable modem from the UK, but it's safely packed away in some storage warehouse somewhere and I can't get at it for another 3-4 months, so I have to buy one now.
eagl