There are at least forty models of digital decoder or receiver (integrated or in a set top box) now on the market.
For up to date information, you can check with your preferred television equipment retailer.
All models will allow viewers to at least watch SDTV in wide screen and will provide some kind of EPG. Some models will decode HDTV broadcasts as well, allowing the delivery of a digital audio signal carrying surround sound information. These HDTV receivers will also offer varying levels of video quality - composite, S-Video or component.
Before purchasing any digital television equipment you should check with the retailer to confirm its capabilities. Different models of equipment will offer different capabilities. Not all models will deliver the entire range of benefits of digital television.
You don't have to do anything until at least 2009.
Until that time all free-to-air television channels will simulcast the same programs in digital and analogue so that they can be received on both old and new television receivers.
So although you won't get the benefits of digital television, you will continue to receive the analogue television broadcast of your ABC TV programs.