Since you only have 1 gig you might as well go for the gigabyte 770 chipset for about $70-80
Then go DDR3
It looks like the motherboard you have should be able to do AM3 CPU's without limiting the bus speed. (or at least it doesn't say that it will, like some of the nvidia chipset mobos from gigabyte)
It also actually supports 140 watt CPU's which would mean you could even stick in the 965 Phenom II
Which means you may be able to try riding out this socket on what you've got (or at least until USB 3.0, SATA 3, and PCI-E 3 all come out)
Try to get some more RAM cheaply, like on eaby or something. You can squeak by with 3 gigs in 64 bit windows for games.