Figure most 1hour, DVD quality streams will consume about 1-2 gig.. so at the maximum/excellent quality, a 200gig drive would get 70-100 60-80 minute captures easily.
Most of the AV systems I use here for recording TV shows or ripping DVD's local- I get a 250-300gig drive and can get >100 hour to two hour images (recorded or ripped) on the disk at a time.