what TV card are you using ? do you know if its been done before ? what output are you using ?
you should be able to with the right card
EDIT make sure you are using the RF output not the pass through, connnect it to your TV card with the appropriate cable then tune the TV channel in the TV card software to the channel for the NTL box, i have no idea what this is but you should be able to scan through the entire range in a couple of minutes