upgrade amd athlon(tm) 64 x2 dual core processor

Solution
There is no point in upgrading this processor even if any processor is available.
Better get a cheap Motherboard + CPU + RAM, that would be much better.

This is what you can get for about 180 dollars, it is very good upgrade to any old computer with inbuilt graphics and a powerful CPU

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: AMD A10-5800K 3.8GHz Quad-Core Processor ($109.99 @ Newegg)
Motherboard: MSI FM2-A75MA-E35 Micro ATX FM2 Motherboard ($59.99 @ Newegg)
Memory: Patriot Viper 3 4GB (1 x 4GB) DDR3-1600 Memory ($23.99 @ Newegg)
Total: $183.98
(Prices include shipping, taxes, and discounts when available.)...
There is no point in upgrading this processor even if any processor is available.
Better get a cheap Motherboard + CPU + RAM, that would be much better.

This is what you can get for about 180 dollars, it is very good upgrade to any old computer with inbuilt graphics and a powerful CPU

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: AMD A10-5800K 3.8GHz Quad-Core Processor ($109.99 @ Newegg)
Motherboard: MSI FM2-A75MA-E35 Micro ATX FM2 Motherboard ($59.99 @ Newegg)
Memory: Patriot Viper 3 4GB (1 x 4GB) DDR3-1600 Memory ($23.99 @ Newegg)
Total: $183.98
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-07-03 12:55 EDT-0400)
 
Solution
New computer at Walmart (say i3 core desktop or even laptop) is only $300, gives you a great processor, more memory and ton more harddrive, but not much in video. So compare that with trying to individually upgrade components of a legacy system isn't worth it.

Personally I would just suggest (for average gaming) getting a off-the-shelf system then upgrade the PSU and GPU and your fine. If your serious about gaming, only systems over $750 or more are doable (see front page of tomshardware.com and the build it yourself systems, it shows multiple gamer systems).