Your CPU is Socket A, Athlon 64 is using Socket 754 or 939. So you'll have to replace motherboard too.
If you do intend to upgrade everything look at Athlon64 X2 6000+ or something from lower end of Core 2 Duo segment.
These are quiet cheap now and pack some punch for games and even work. Memory shouldn't be below 1GB these days.
If you don't need fancy graphic card, take motherboard with integrated one, otherwise GeForce 7300GT/7600GT is still a very cheap and decent card (though don't expect too much from it). For more look at GeForce 8500GT or Radeon x2600 Pro.
Everything is per your need.