[Halcyon]

Cat 5 cables running alongside each other is fine.
You just have to take a look in one our cabs at work and there are tonnes of cables all over the place.

It's power (electrical) cables that you should avoid placing next to ethernet cables.

Another thing to bare in mind is you should get specially shielded cables if running cables outside or underground.

Oh, and why not go cat 6 just to be on the future proof side.