OK. So you got a HSC mark of 58 for English Standard and a HSC mark of 86 for Japanese beginners?
This is based on an average mark, so if you do better in one subject you can do a little worse in another. Also, this is all a prediction based on the 2004 marks. Don't take it as absolute, it's just a rough outline of what you might need. So, if you need a 75 UAI:
For IPT you'll need about an 87 HSC mark, which is just below the 90% group(You need to be near the top 10% of students doing that course).
For IT you'll need about a 92 HSC mark, which is about halfway between the 90% and 99% group(You need to be in about the top 5% of students).
For General Maths you'll need about an 85 HSC mark, which is just above the 90% group(You need to be within the top 10% of students doing that course).
As for Standard English. Let's say you did it again, and got a HSC mark of 75 (90% group...). These are the marks you would need for a 75 UAI in that case:
For IPT you'll need about an 84 HSC mark, which is between the 75% and 90% group(You need to be in about the top 20% of students doing that course).
For IT you'll need about a 90 HSC mark, which is just above the 90% group(You need to be in about the top 10% of students).
For General Maths you'll need about an 82 HSC mark, which is just below the 90% group(You need to be in about the top 15% of students doing that course).
So there you go. Even if you get 15 more HSC marks in Standard English, the required marks only drop by two or three. Plus, you've got the extra time required to complete the course, which might make quite a difference to you. But then, you already know the course, so you could probably do a lot better the second time around.
If you think you can do better than a 75 HSC mark in Standard English, let me know, and i'll recalculate the required marks. Otherwise, I don't really think it's worth your while doing it again...
Ask away if you want anything else too. I hope that this helps.
In any case, good luck.