The two images are slightly magnified identical-sized small crops of a 40D JPG and a 450D JPG at ISO 1600 viewed side-by-side in Survey mode in Lightroom 2.0. The screen capture was saved with FSCapture at 100% JPG Quality.
Compare noise in areas of similar brightness.
This is just a rough comparison because the camera contrast and sharpening parameters, temperature, exposure length and any number of other things are different, but it is still useful to see the noise is the same order of magnitude.