Has anyone else noticed a problem with the onboard "Intel
Pro/1000 CT Desktop" ethernet controller only detecting a 10 MB
network, even if you're on a 100 MB network?

How can you tell? I have a P2P with three computers (two now since the
notebook is in the shop), and I have no problems that I'm aware of.
It says so in the Intel PROset software that came with the
motherboard. There's a button that says, "Test Link Speed". When I
test it, this is what it says back: "A Category 5 cable is required to
run at 1000 Mbps. The cable connected to the device either has only
two pairs or has faulty wires."

Also, the 100 light on the router is turned out for this port
- only the 10 is turned on. FYI, I have tried switching to another
jack and also tested the cable with another computer (works at 100
there). There's also a "Test Cable" button, and that doesn't detect
any errors on the line.

The funny part, is I made this particular wire myself using
Cat5e cable, so it should be good for 100 or 1000. I don't have any
problems with any of my other computers reaching 100 - I'm not really
going for the full 1000 speed here (I personally thing that's a waste
of time until hard drives become faster).

Their stupid software thinks there's a bad wire or something, and I tested
all 8 wires myself, and they're fine. I even tested it with multiple patch cords.

Is it generating errors?
No there are no errors.