@qtjenni, from what I've read about MCE on AT&T, when you do the STB setup you may have to go through the process for Media Center to learn your new remote.
@Dr.Dave, I've been running windows media center for 5+ years as qtjenni above said (I am the aforementioned husband in her post), and have learned remotes from three different Sasktel STB remotes (The PACE DSL4000 ones, the ones they had after those, and these new Motorla boxes) and it has always worked.
It's just since the upgrade to Microsoft mediaroom that media center refuses to learn the new max remotes. It learned the previous generation's remotes without fail.
The only thing I can think to try is update the PC with all the latest windows updates to see if perhaps theres an update that adds some additional capabilities to media center.
The conspiracy theorist in me thinks that this is planned by Sasktel so that we'd be forced to buy their expensive DVR service.
Ideally, I'd like to use my three xbox 360's as set tops for my max service and switch to their DVR service just out of convenience. I know 360's are compatible with media room as set top boxes, as I've seen this in action on a tv provider in the states (Can't recall the provider at the moment though).
Additionally, one thing we noticed last night is the new remote will change channels on the old software (we had an un-upgraded box that was not connected the night our upgrade happened) so I see no reason the existing programming in my media center shouldn't be able to change the channels...weird...