Hey man
I fucked up my HSC in 2001 - got a UAI of 69. Most people give you a patronisingly rudimentary "oh that's not bad!" Although if your result didn't get you where you wanted it, then yes, it is that bad...
I'll tell you the best way to get into university...
Repeat the HSC. That's what I'm doing, that's what almost everyone does (people aged 16 to 63 are doing it at TAFE). You can do a Tertiary Preparation Certificate (TPC) if you want, but I'm certain it can't get you into the higher courses (Law, Medicine, etc) because everyone who wants to do such things is sitting the HSC. You also have to be 20+ to do the TPC. At TAFE, you can do HSC topics in one year by doing the preliminary course at the same time (it's called a combined program) and to be honest it's sweet fuck all in the way of extra work. I'm doing Geography and Economics CP.
You might want to look into the concept of a Limited UAI as well.
Trust me - repeating is fucked. As sad as it is, there are a lot of people out there who do look down on you for it. Without stirring racist sentiments, I'd like to add that some cultures look down upon repeating more than others. Personally, I don't mind. It takes one fuck of a lot of guts to admit you fucked up and go back to correct it. I was a rebellious waste away drug addict in year 12, and I don't even feel like I sat the HSC first time round. If you're worried about repeating,
lift your game now son!. Most of my friends are in their 2nd year of 3 at uni. Others are in their 2nd year of 5. I'll be starting next year so I'm well behind the times.
But hey, I'm happy.