Yes, they should be fine. The cable is a shielded design. The Cat 5 is twisted pair and any noise that's induced in one wire will be induced in the other wire and will cancel out.

RG-59 for regular cable TV, RG-60 for high definition.

If you do run the Cat 5, be aware that it typically only uses two of the four pairs of wires and that you can use one of the extra pairs for a wired phone.

Have you considered using a wireless router for the internet? Then you can take your laptop into the garden. :)

I wouldn't run the power through that same conduit.

Here is a link that might be useful: Wiki for cable types

you will be fine running the low voltage lines int eh same conduit, just keep that conduit at least 12" away from teh power feed.

you absolutely do NOT want RG59 for any antenna signal. with teh change to digital broadcast your signal may already be weaker than before. get the RG6 and be done with it.

and although you can run voice and data on teh same cat5 cable, i try to stay away from it where i can.

what about power? is your shed bonded back to teh house ground system? if not it must be since there will now be an additional ground path between the two. best case scenario is the ground loop induces hum on both lines. worst case is the shed equipment tries to ground back thru teh ethernet/tv cables and a surge cases a fire.

sicne this conduit will be runnign outside, you need to run outdoor rated Cat5. the conduit WILL eventually fill with water due to condensation, so unless you want to replace the cable every couple years spend a little more money now.

thanks guys.
i got really lost about the ground loop stuff...
wouldnt the power (which runs through a seperate pipe), have its on ground? it is also run through a pipe in the ground, so why would the power try to ground through a pipe not connected to it?

Here is a tutorial that helped me a few years back.

Here is a link that might be useful: Detached garage wiring

and also: couldn't i run the pipe on a slope (once the pipe hits under the house it isnt underground it's exposed). once it hits under the house couldnt i drill little holes on the under (or over?) side of the pipe to allow the condensation in the pipe to evaporate? or jsut for the built up water to just drain out? or will it lead to more problems?

Your power lines will provide a ground path and prevent the ground loop problem. I think it would be worthwhile to drive a grounding rod into the ground and bond that to the ground of your electrical service.

There is no reason not to run a phone connection over one of the unused twisted pairs of the Cat 5 cable. I went to two different electronic tech schools and I still work in the electronics industry. I have personally done exactly this in my house. No issues.