Do you need a monitor, keyboard, mouse, speakers, or headset within that budget?
If you're just buying a tower, and that's US dollars (not Australia or New Zealand), you should be able to get an excellent setup for that much. Especially if you can wield a screwdriver without stabbing yourself, which is all it takes to build your own.
Look for:
Core i5 2500, or better yet the 2500K (easier to overclock) CPU.
LGA 1155 motherboard with whatever features you need. (USB 3.0 and 6Gb SATA are becoming common.)
nVidia 560Ti or AMD HD6950 GPU. Don't settle for less than the 1GB nVidia 460 or AMD 5850.
8GB DDR3 RAM. DDR3-1600 with CAS 9 timing is common and cheap now.
Western Digital "Caviar Black" or Samsung "Spinpoint F3" hard disk, bigger than you think you need.
Pretty much any DVD burner; they wear out and have to be replaced anyway.
A top-notch power supply of at least 500W. Corsair HX or TX series, or anything from Seasonic, is excellent.
A case that it all fits in. Antec and Lian Li make nice boring cases. NZXT makes nice cases that are less boring. Coolermaster HAF cases are excellent value.
Windows 7 64-bit, either Home Premium or Professional.