Depending on your expectations, it may not be possible.
At best, you may be able to record what channel the cable box is tuned to at that given moment, and the cable box is turned on. This assumes that the yellow/red/white (YRW) analog connections on the box are active.
To verify if they are active or not, I suggest you connect them to an available YRW input on the TV and select that input. If they do work, you should be able to tune in TV channels via the cable box and watch them on your TV.
If they don't work, you need to check with the cable company as to why they don't. Perhaps their hardware is set up as an either/or situation between digital and analog. Or, they simply don't work. In either case, you need to work this out with the cable company.
If you CAN tune in channels with the cable box and view them on the TV using the YRW analog cables but the DVDR won't record, then it's an issue with the DVDR. Perhaps the manual or Toshiba CS might be able to help.
Good luck...