I would recommand something like this:
AMD Athlon xp 3200+ (barton core) - $320
Gigabyte 7VT600 - $130
Gigacube Radeon 9600XT - $260
512 DDR 400 - $150
SB Live 5.1 - $70
They r the main features u should be watching for when upgrading a pc. As u can c from that it's pretty cheap and that would be a good pc. You could get that now with your $1k and if u wanted just boast the performance with a bit more ram etc.
Them prices are just estimates but I'm pretty sure they will be very close to that.
www.scorptech.com.au www.auspcmarket.com.au www.sydneymetrocomputers.com.au
These are some of the sites I look at hardware. they are all australian sites. I'm also about to buy the radeon 9600XT from scorpion technology, I've heard good feedback from their company.
That motherboard that I recommanded is the one I'm using atm and it's good enough but you could just look around and pick one out that seems to be better to you.