With regards to photographing an LCD, it's mostly down to technique rather than how good the camera is.
I actually started writing a guide on how to do this the other day, with part 1 up on my site now: http://sr-388.net/2007/02/23/how-to-photog...el-display-pt1/
This was using videogames for its examples (another hobby of mine) but it applies to anything. Other than what I have written so far, the most important thing is to avoid over-exposing the image.
Out of interest, is this iMac a PowerPC (G4, G5) or Intel machine? I don't remember having this problem on my old G4 Powerbook (though I didn't have Aperture back then) which is why I believe the problem is with ColorSync on Intel (or at least Core2Duo) machines.
It was my understanding that if you have an image, do all your editing etc, and then convert to sRGB and export it, tagged with sRGB, it would look the same in both managed and unmanaged applications. (as unmanaged treats everything as sRGB) Doing that on this laptop doesn't work. I'm quite sure that it did on the Powerbook. (but it has been a long time since I used it now)