If you run Cat5 or Cat5e from inside to outside or vice versa you will want to use a gel filled cable (outdoor rated). Even though you are going underground it will help ensure the longevity of the cable (if you are worried about it). 100 meters is the max length, but I've seen it work up to about 150 meters. You lose collision detection after 100 meters so your packets may get a little messed up on transfer! Remember any time you run cable in conduit pull in a piece of twine for future cables!