just use PVC, its easier to work with and less conductive/corrosive than aluminum. as far a EMI you could run your cat 5/6 cable right next to a coaxial cable and you still would probably be getting more EMI from the power lines that run down your street than compared to whats coming out of the coax.
True enough, especially since coax is self shielding.
That being said, cat5(e) or cat6 is technically a balanced transmission line, just like a phone line is. The twisted pair nature of it means that interference introduced on either lead is canceled out through something known as common mode rejection. This works for many things, including those fluorescent fixtures. When in doubt, run the cable at right angles to the potentially interfering cable if one has to cross over the other.
The only times I've had to install shielded 5e or 6 is in *one* industrial setting and a few medical and lab settings. In the latter cases it was because they were more worried about leakage from the
cable itself screwing with sensitive lab instruments or medical equipment (like heart monitors and EEG equipment), not the local equipment causing interference on the cable.
People who are that worried about signal degradation due to outside interference should just run fiber. *grin*
