For basic Cable TV station viewing, you can hook a 2 way splitter to the incomming cable line. One output of the splitter goes to the cable box which is connected to the tv. the other output of the splitter is connected to the slingbox pro hd internal tuner's coaxial input.
The method above allows your slingbox to watch basic programming independant ogf the local cablebox/tv viewer. However in order to watch any premium station (hbo, starz, cinimax, ppv, etc) independantly, you would have to connect a dedicated cable box to your slingbox.
You can however connect as I indicated above in the first paragraph, and also connect your existing cable box to your slingbox via component video cables. this would allow you to watch basic programming via the slingbox's internal tuner, but also give you the option of watching the cablebox along with the local tv viewer.
Again for total independant viewing of ALL stations, ,you'd have to get another cablebox and dedicate it solely for the slingbo'x use.