Ok, another person who doesn't know the facts and sees the need to talk out of their rear end.
The standard for Australian digital TV has been set (to the dismay of many who wish it could be changed). But there is very very very little chance of something different happening, it's in the legislation. So no, everything now should be mostly be compatible (some newer features like interactive tv may not be fully supported by the software, but it isn't a feature really used in Australia at the present time - so the tv channels themselves will definetly be fine). Actually a good reason to buy now is that there's rumour that the government wants to put copy protection on tv tuners so you can't record -> piracy.
Analogue tv is definitely shutting down in 2008 just the possibility (and at this rate it won't). But yeah, by then it dtv will be a lot cheaper and it'll be starting to get totally phased out, especially with the new widescreen tv's getting for popular.
Keen