I've got one of these connected to a Samsung STB and it works fine.
If you have any problems, you need to flash to a
working firmware version. There are two beta versions, 1.45.7 and 1.51.0 which are better and more stable than the one on the Linksys website. They can be found
here. Have a good read of the thread first.
I've registered to NTL while connected to my PC and then cloned the MAC-address within the router.
Let me know if you have any more questions and welcome to the SX41 adventure.
BTW: Make sure that DMZ is disabled within the firmware, unless you want no protection, otherwise use ports 1 to 3.