This is from probably the best place you could buy from in Aus, for decent parts:
Intel Core i7-920 = AU$389
Intel Core i7-950 = AU$697
If you just want an upgrade, don't bother with quad or i7, get a dual core, many applications don't use quad at the moment, my new family/gaming pc runs the Nvidia 260 and the Intel e8500, in my opinion get the e8500, really good part, stock it runs at about 2.8Ghz but can be O/C'd to 4.2! Provided you have good cooling.
If you were to go all out, get the i7-920, I definitely when I build my beast in the near future
I'll post my full pc specs in my next journal
So for ram, definitely upgrade to atleast 2GB of DDR2, if not more, its cheap as chips, the 260 is the best value for money card out now, theres still the 8800 and 9800 series's, which are very cheap now costing less than 125$AU
So there you have it, stick with a 8800, 2gb and the e8500, and your PC will last, and allow you to play the latest games and you won't have to upgrade your mobo (I'm pretty sure, someone correct me if I'm wrong)
BTW, I've never had any trouble with my POS ATi card in my laptop which I use for mapping with Hammer, or am I unaware of the problems because I'm still a n00b at mapping?