I have a D-Link Router/Switch set up and I have my desktop which connects fine at 100.0 MBps but on my other desktop with has a longer CAT-5 cable, connects fine but only at 10.0 MBps and user reports very slow, is that a Ethernet card problem, CAT-5 problem or settings problem?

on the 10mb computer, have you looked to see if the network card settings are set to autonegotiate, and full duplex?

As suRoot suggests, check the link speed and duplex settings in the network card's hardware properties. Also double-check that the card is using the correct driver.

If there doesn't seem to be a problem there:

- Switch the Ethernet cable with one that known to be in good working condition. Unless your cable is approaching the (approx.) 300' limit for 100Base-TX Cat5 wiring, length probably isn't your issue. However, a CAT5 cable can become incapable of operating at the full 100M if it has been excessively bent, kinked, stretched, etc., or if the RJ-45 connectors aren't crimped down tightly/correctly.

- Check the RJ-45 sockets on the card and router; make sure the contact "fingers" of the sockets aren't bent/damaged.

- Make sure the CAT5 cable is not running near sources of possible electromagnetic interference. Flourecent lighting circuitry, for example, is one very common culprit.

- Try another port on the router; you may have a "weak" or failing port.