Cheap but powerful 64-bit system?

AMD make cheap 64bit cpu $25
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

on the bottom left you can make it a cpu/mobo combo for $70

AMD x2 3600+ CPU
Foxconn 690 Motherboard
512 or 1 GB of the cheapest PC26400 you can find

All from newegg. The mobo and cpu has free shipping. I am putting together a budget PC for someone right now and I really like these parts for the price.

Cooler Master Centurion 5 - 29.99 after Rebate
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Antec NeoHE 430 - $40
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Intel Pentium E2160 1.8GHz - $95
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
GIGABYTE MB GA-P35-DS3L - $87
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Kingston 2GB (2 x 1GB) DDR2 667 - $86
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
GIGABYTE 7300GT 256MB - $70
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Price: $408 after rebate  

That should be a pretty good basic system.

I would go to Circuit City or BestBuy and get whatever they have around $500, ideally something that happens to be on sale. Just make sure it says Core 2 somewhere. You could build your own PC yourself from parts but this way it's cheaper and safer and faster and you get a warranty.

Or check one of the threads with titles like "help me pick parts for a $700 build"...

What OS have you got? If it's Vista you do need good video.

What software have you got? Just curious if it's something that works best on a quad-core processor.

How much money are you willing to spend on the PC itself (don't include monitor, speakers, keyboard, mouse)?