the ram on a video card has no issue on the motherboard. the motherboard itself will have agp or pci 1.x or 2.x slot.
if it the older 1.x slot some of the newer gpu would be bottle necked from the lower transfer speed.
Any PCI express GPU would fit into a mother board with a PCIe slot as yours does and it supports upto 2GB gpu memory so you're fine there too with 1GB.
The motherboard supports DDR2 but the GPU is DDR3, they wiil work but the GPU will only run at DDR2 speeds, however, there is little difference to this unless you're looking at the very small details in hardcore gaming
I would suggest getting a new PC
as i also have a Gigabyte 945GCMX-S2 775 socket Mobo which only supports DDR2 RAM
i have a XFX 5450 which i placed in the case 2 years ago
So ya you can place a 5450 in there but it won't play most of the available games smoothly