I've seen 100Mbps ethernet work happily at 120m on cat5e and 10Mbps work at well over 150m but I wouldn't recommend it if you can avoid it!
As shtu says, there aren't many houses where you're going to need a single run of over 100m, I cabled a 15,000 sq ft house a couple of years ago and I even managed to do that with only two concentration points.
My house is 3,500 sq ft and my longest cable run is less than 30m - but the cabling did go in before the ceilings went up and the walls were plastered, which made routing very simple.
Comms is hard 