I've a 100mbit switch that is verified to work properly on all ports via small patch cables, the jacks and plugs were verified to be CAT5 grade, I made certain the wires have no pinches or pressure on them and are terminated no more than 1/2 inch to each. Each wire runs no more than 25 feet to the switch. All NICs are verified through Linux and DOS tools at 100/Full Duplex.
However, NETBEUI communication is painfully slow, not anywhere near 100mbit, and IP based games are choppy and have frequent timing event errors. I ran a few throughput programs (LanMark and Anasil)found from http://www.downloads.com and discovered I was only getting 1mbit.
I read on this forum that stranded wire should be run no more than 10 feet and I recall my wire to be stranded. I suspect this is the core of the problem, but to compound it, the wire is unshielded and the wires are not tacked up in the attic yet, so it is possible they are parallel with other wires up there, picking up stray signals.
I think I will replace all my wire with solid CAT5, and possibly get it sheilded. What do the more experienced folks think?