I upgraded the guts of my computer (i.e. kept the drives, monitor, keyboard, mouse) a couple of weeks ago in Aus, and here's roughly what I got with rough prices:
MB: Asus A8N-SLI deluxe $200 - This MB rocks, I know several people with one, and it is highly recommended. It uses the nForce 4 chipset.
CPU: AMD athlon64 2700+ $350ish - It seems that dual core's are not really worth the price at the moment unless you do a lot of multitasking
Graphics: XFX GeForce 7900Gt 256Mb 520Mhz (not sure about the speed, but don't get the super-overclocked ones as they die very easily) $450 - Seems to be going very well, not top of the line, but you can get 2 of these for the price of one 7900GTX. It is possible to get a 512mb 7900GT for around the same price from inferior brands, but they are very rare.
RAM: go for 2 gigs if at all possible, I've only got 1gig, but really want a second.
Antec case, not sure which model but it was $170ish, and is very big and roomy and has funky blue LED's (mind you, LED colour shouldn't be the deciding factor).
One place you should check out is
http://www.tomshardware.com/ a very useful site with reviews and comparisons of lots of stuff.
Hope this helps.