Ok i've got an HD compatible TV (Tevion from Aldi wooo!!) which outputs higher than SD, probably 1080i (or p, whichever one's lower) and it allows ggood visuals from my 360 and ps3.
i'm certain it doesnt have a tuner in it so I'd need a settop box?
the tv aerial is crap and i get heaps of snow, does this ened to be fixed? one of the reasons i dont bother fixing it is cos 9 turns out ok (and thats where the footy is!). running a crappy aerial through an HD box, will that give a better pic or just HD with snow?
If it's a tevion, I highly doubt it'd have a tuner in it. You'll need a HD set top box. By the sounds of it, your tv will accept a 1080i signal, but the screen resolution is probably 480p (as most 720p+ tv's come with an inbuilt tuner). All of that is irrelevant though, you'll get much clearer picture with a digital set top box.
As to whether you'll get snow or not, digital never gets snow, but it gets "artifacts", basically blocks of picture that will have a glitch in it, and sound popping etc. That is all dependant on your aerial, but hard to gauge depending on your analogue signal, generally there should be an improvement. Your best bet, if you want HD television is to buy a set top box and see how it performs, if the picture is still an issue, you may need to get your aerial re-aligned which will probably cost around $100 depending on the time it takes.