[Solved] Low- Mid-end system - some random questions

Hi all,

I'm building a new computer from scratch for someone, and I'm wondering whether I'm on the right track with the parts I'm choosing. The system probably wont be required to perform too many strenuous tasks, the most stressful would probably be some light gaming in the form of Sims 3 and a few others. Some light future-proofing would be a good idea as well, because its unlikely that the machine will get an upgrade anytime soon. Basically I'm trying to get the best bang for my dollar (Aussie dollar, by the way). So far, I think I've settled on the following parts:

GPU - Radeon HD 4670
RAM - Corsair XMS2 DDR2 4gb (CM2X2048-6400C5)
HDD - Western Digital Caviar SE16 WD5000AAKS

Apart from that, I was thinking of getting the new Athlon II X3 435 (heard some good things about it), but it will depend on whether it is available in Australia by the time I'm building the system, which is probably early December.
The motherboard is something that is stumping me, although obviously it will depend largely on what processor I go for. From what I can tell, the price difference between AM2+ and AM3 is negligible if it means better performance in the long run. Should I be going for the AM3, and DDR3 RAM, or the slightly less expensive AM2+?
Also, from the above description, how much power is the system likely to need, and are there any recommendations for solid PSU's that can cover it?
And finally, are there any recommendations for a cheap(ish) good quality case, or am I wasting my time researching this aspect, and would be better off just picking something up when I see it? Basically no frills, but not complete crap either.

Thanks in advance for the help

I agree with dirtmountain - DDR2 has jumped significantly recently. If I was building now, I'd go DDR3, so if I needed to add more or replace it, it'd be cheaper (as DDR3 is coming down, and DDR2 won't ever be as cheap again).