It all depends on which box you have. If it's a Pace 4001, 4010 or Samsung then you can use any videosender. It doesn't matter that you aren't sending video, you're just using the reverse path for the remote control signals. Alternatively, use a normal
remote control extender (in particular the AV08554)
Things are more complicated if it's a Pace 1000, 1010, 2000 or 4000. These use an unusual infra-red signal protocol, based on the IRDA standard. To get this to work you'll need either:
1) a DigiEye DG100DE:
http://www.digisender.net/dg100de.htm
or
2) any videosender or remote extender
plus a RedEye infra-red translator:
http://www.redremote.co.uk/
Perhaps, one day NTL might get their act together and release the
RIR100