Fast ethernet (100baseTX) uses the same two pairs as 10baseT. It most definitely doesn't use all 4 pairs. If it did, then it would be pretty miraculous how I've been running 100baseTX all these years without connecting two pairs. You can check documentation all over the place, including CISCO to verify this.

My first guess regarding Roger's problem would be bad connections, not broken wires. I have always used solid core wire and have used both a punch-down tool as well screw-down wall terminals (which is what I'm using right now).

When putting in a new wall plate at a friend's house we ran into a similar problem. The replacement plate was not like the original. It was meant to have all the pairs wired IN ORDER. ie. you didn't skip pin 4 and 5 when wiring the TX lines. This was a bang-your-head-on-the-wall scenario once we found out.

Continuity testers are nice, but if you don't have access to one, you can also isolate the problem by using different runs of known-good patch cord, skipping various connecting segments as you isolate.

Bottom line: I would check the wiring requirements of the wall plates.

And for good measure: standard is: 1 & 2 are RX (+ and -) and 3 & 6 are TX (+ and -)

Bruno