freitasm: There's not "polarisation" on DVB-T. I assume you are talking DVB-S?
Anyway, for the correct frequencies in each city/town, look at this guide (it's a sticky in our forum): http://www.geekzone.co.nz/forums.asp?forumid=83&topicid=19328
I think spk18 was talking about antenna alignment, and whether you have the elements horizontally or vertically aligned. If you look at the the Freeview|HD frequency table on the freeview website, the frequencies either have a V or a H suffix. It also explains why Wharite (Manawatu) and Mt Kaukau (Wellington) can have the same freqency and not interfere with each other.
Of course, I could also be speaking utter crap...