the epg data is so that you and your pvr know what is on at what time and on what channel. If you select to record a series or an individual show, then the pvr will know what channel the dstv decoder would need to be set to for this to happen....are you with me so far?
now, when the time comes, if you have programmed in the ir codes for the dstv remote correctly, and have a suitable ir blaster attached to your pc, the pc will send the ircodes out and the blaster will flash accordingly, effectively emulating the dstv remote control, and changing the channel on the dstv decoder to the one desired so that the show can record.
as far as the dstv decoder is concerned, it "saw" the correct infrared code to change the channel, and it believes these codes came from the remote control, but in fact the pc sent these codes out via the irblaster to enable a particular program on a particular channel to record at a particular time (as dictated by the epg)
tha is why you need an epg, an irblaster, and a tv tuner with a compatable frontend (mce2005, media portal, showshifter etc)
once you have it set up, you can be at work, and your tv will merrily send out ircodes at the correct time, the dstv decoder will change channel as needed because of these codes, and your shows will record.
without an epg, you can only do vcr-style programming, e.g. at 6:30 everyday record on channel 62.
with an epg you can say "I really like rugby and chuck norris films, my wife like egoli, and the kids love spongebob, record anything that features rugby, chuck norris, egoli or spongebob on any channel whenever it is on or only on weekdays, or only first runs, or only repeats, thanks buddy p.s. make sure the rugby takes priority over spongebob if they are on at the same time"
and voila! as if by magic when you get home your pc has "harvested" the daily programming for your favourite items and they are all waiting for you to watch. So you effectively create your own tv channel with your favourite programming to watch when you get home, and you can just ffwd through any commercials. Of course, while you are watching stuff that it recorded for you during the day, the pc and dstv decoder pair and still recording more items so that you always have stuff to watch. You will get to a stage where you no longer use the dstv remote, or watch live tv....the pc will take care of your viewing habits and continually harvest programming you like...putting it into a queue for you to watch when time permits.
that is the basic idea.
as you already have mce2005 all you need is the remote+receiver that ships with it (I believe they are around R600 in s.a., or ÂŁ20 in a non-ripoff country)...this comes with the required irblaster to enable channel changing.
now stop watching television in the last century

pvr's will change your tv habits and give you more free time.