G'day!
Well you have a helluva lot of options. I'd suggest a PIII 800 with an ASUS CUSL2 board. That would give you a very stable platform.
You should be able to pick the combo up for under $700 AUS.
my only credential here is that i'm going to put this machine together myself. i'm going with the asus cusl2-C (without video) and a pIII 1.0gigasaurus....however, i might go AMD for the next one.
im using the asus cusl2 and a pentium III...i decided to get it a few months back. its definitely the most stable system i've had. i love it...i bought the two seperately from different companies on pricewatch.com b.c the combo deals are usually more.
-Tom