The laptop will be easier. You'll need some sort of active converter/downscaler between the output from the VGA port (maybe something like this?) and the ones accepted by the TV, then an RF modulator. I don't know if this is going to add input lag, which would defeat the point of using a CRT to begin with.

As for the desktop, I think you can use a passive DisplayPort to HDMI cable and the same principle is going to apply with an HDMI-to-composite converter. Again, input lag is likely.