Hardware- and software-wise, you're right where you need to be. you need only a tuner (and, possibly, a remote if you want one.)
If you were in the US or Canada, it would be easier to advise you on a tuner (that's where the majority of us are.)
But, you're in Australia - y'all have a different broadcast format than we do (as you said, PAL), requiring different tuners. And, there's some funkiness in getting working EPG data into Media Center for you (MS has no EPG data for you guys); but, it is doable.
I'd recommend posting the tuner question (after a quick search, of course) at the forum that's targetted to you: the Australian Media Center community at http://www.xpmediacentre.com.au/community/forum.php
They'll be able to help you out right quick on those two points.
I'm not trying to kick you out of here - not at all. But, they're a lot better suited your your particular situation (a potential MC user in AU, needing tuner advice) than we are.