Any interest you pay on your mortgage is tax deductible. The house itself is tax depricatable. Expenses such as pm fees, maintence, improvements may fall in either the deductible or depreciatable category depending on what it is. I would recommend keeping good records and tracking down a GOOD "property wise" tax accountant, to help figure it out. Too many accounts don't actually understand all the in's and outs of property investment and can cause problems with the ATO claiming the wrong things.

Positively geared, means you are making a profit off the property after all expenses are taken into account. You need to pay tax on this profit.

Negativley geared, means you are making a loss after all expenses. This loss can bring down the amount of tax you have to pay.

What kind of mortgage do you have? Does it have an offset account? Does it have a redraw facility? If it has a redraw facility have you ever used it?
An offset account is great and means that you should have no issues with the interest on your mortgage for tax purposes.
A redraw facility on the other hand can cause serious problems with the ATO. If you have used the redraw facility for non-investments purposes (ie, personal use) then unfortunately that % of the mortgage interest is no longer tax deductible. It can get pretty complicated, hence having a good accountant to help sort it out.

The other thing to keep in mind is the capital gains tax implications, when you go to seel the property. If you sell now, you will not have to pay any capital gains tax. If you turn it into an investment property you have six years before you incur capital gains tax, unless you buy another primary place of residence in that time, in which case you will have six months to sell after buying before incurring capital gains tax.

How old is the property?

I am pointing all these things out, but you will have to run the numbers to figur out if keeping and renting or selling would make more sense financially. Personally, I believe in never selling real estate once you own it, if you can help it - but you definitely need to run your figures.

There are other things to consider such as the emotional side of things, are one someone who becomes attached to a house and would hate to see it damaged? Because although the majority of tenants are reasonable people, the fact is they are unlikely to treat you house with the same respect you would. Wear and tear is higher in rental properties then in owner occupied properties, and although bad tenants aren't as common, they do exist and it is a possibility that at some poin you will get stuck with one. LandLord insurance is a neccesary expense IMHO. This will cover any rental defaults, or damage caused by bad tenants. Hopefully you would never need to claim, but the majority of LL's I know have had to make a claim of some sort over the years. I have also know LL's who don't insure, but they have a large enough asset and cash base to cover such costs themselves (not many people are that fortunate).

Hope this helps.
Feel free to pm me if you have any q's. I also know of a good property investment forum that is sually very good at answering questions if you would like me to pm you the address.