Sorry to say, but Athlon 64 systems are not numberous currently. The cheapest one you'll be able to get will be $1800 base price (Sager 4750). At this price you will get a small slow hard drive.
The maximum amount of RAM you need is either 512MB or 1GB. 512MB is idea, best bang for buck. Unless of course, you may get only 256MB and then upgrade it youself. You can do this with both the RAM and hard drive. Order the cheapest you can get when you buy the notebook, then get the best you can afford from
Newegg or
ZipZoomFly. THis is the better option for you. Then you can sell the original hard drive and RAM.
Anyways, the 4750 comes highly recommended. Check out the
Sager General and
Sager Reviews forums to learn more about it.
To get a good 4750 with what you want would come to $2000. The other notebook you can consider is the Acer Ferrari. Sorry, but no notebooks with Athlon64 and your requirements in you budget.
You don't HAVE to get an Athlon64. Centrino systems perform incredibly well... games like Far Cry and Doom 3 will run fine on them. So you may want to consider getting a different processor... unless you stuck on the 64 bit.
Come November, I bet Athlon64 systems will have increased dramatically and you will get a system you want for your price.
Phew that was long

. Hope that helps.