Getting EPG data is not a big deal, but may be costly if you plan to sell services based off it, e.g. a single Tribune (EPG data monopoly in the US) EPG data access costs around $10K. However, if you are developing apps for non-commercial purposes, e.g. open source, you can get this data for $20/year at http://www.schedulesdirect.org/.

The real problem is to access the video stream. Currently this is viewed to be illegal (see the lawsuit in 2001 that pretty much sank ReplayTV, http://www.eff.org/cases/newmark-v-turner).