Comparing the above photos, it definitely looks like the camera does a lousy job at higher ISOs. I'm not sure if that has more to do with the sensor or the amplifier, but software can only reduce the effect at best. Post-processing with software like Noise Ninja will help, but that's not free. Mostly it's the camera's firmware that can make the biggest difference in reducing this noise. This is the biggest problem with tiny sensors, especially ones that try to cram a lot of pixels into that tiny area. The signal to noise ratio at higher ISOs gets pretty bad...
Try to limit your pictures to bright environments to get the best results.