You can certainly play your DVD movies through a DVD player connected to your SB to sling them through your SB. But I don't know of any way to hook your hard drive up directly to your SB -- not only are the cables all incompatible, but you would need to have some sort of "remote control" that you could use from your computer somewhere else in Internet Land to control the playback from the hard drive. Perhaps there is some sort of DVD-like media player that you can incorporate your hard drive in to? And then connect this DVD-like device to an SB in the usual fashion?
What I understand from your post, is that you would like to know if it's possible to stream from a hard drive using the Slingbox.
In this case, for you to be able to connect to the Slingbox, you need to connect it to an actual Set Top Box such as DVD, Satellite Receiver, Cable Box or DVR.
Other than that, we can't assure that will work properly. Besides that, you can check the following links about the supported Audio and Video Sources.