It is 3gb DDR3. Should be ok for an old 2010 system with no dedicated gpu.
Will overheat when doing even basic stuff due too the blow not working. You can just grab a random intel or amd stock heatsink and mod it on there.
This gt 640 has an extremely small heatsink on it and without the fan it won't be able to keep itself cool. Adding a regular fan on top will do little since the platic shroud is open all around and that fan in there is specifically made to blow in a certain direction.