The hotel is called the Hyde Park Inn and it's on Elizabeth St opposite the War Memorial. That makes it every convenient for the CBD, Oxford St., Darling Harbour, and even King's Cross, if your tastes run that way. I've stayed there a number of times and it's been excellent. The front lobby is no more than the desk, but the rooms are large and come with a small kitchenette that they stock with breakfast stuff every day. There's a reasonable Italian restaurant adjacent to the lobby. All the rooms overlook Hyde Park and have a small balcony, so the upper floors are best.

I was just about to make my reservations and notice that the prices are lower than last year. I usually go for the deluxe, but I don't know how much it differs from the standard. For $130 AUD in that location you can't beat it.

Here is the URL for the booking agency. They're Singapore based and have always been very efficient:
http://www.holidaycity.com/hydeparkinn/index.htm