Again, I'm new here and looking at the first page of posts I didn't see this listed so I thought I'd drop this idea on everyone.

Most network adapters by default are set to "auto-detect" the network link speed and duplex.  Like most things that "automatically" happen, it doesn't always work out so great.

Things can appear to be working fine, especially with SOHO network equipment that is very limited in its' logging capabilities...but you may have line errors out the YIN-YANG (this is bad).  You wouldn't be the wiser because your router/switch is not capable of reporting these errors to you.
There's a long list of possibilities on these errors from excessive collisions, late collisions, FCS errors and CRC errors...these will slow down your network.

Fortunately there's a real quick and easy way to avoid this entire mess.  Manually configure your adapter for the link speed and duplex.  This can be done in xp by right clicking on "my network places", choose properties.  Locate and right click on your local area connection, choose properties.  At the top there should be your Adapter...THE KING, next to it is a button that says "Configure", click on that bad boy.  A dialog box will pop up, choose the "Advanced Tab" and you should see an option for Link Speed and Duplex with a drop down box on the right.

Consult the documentation for your home networking gear for the correct speed and set it on all of your computers.

HTH

it can actually get so bad that some hosts will lose connectivity, that's when I discovered this.

Always used auto-negotiate because it was quick and easy, didn't have to worry about configuring anything.  Until one day my newly clustered servers kept dropping off of the net.  Looked through the machines in and out and couldn't find any cause for it.  Swapped out NICS, swapped out Lines, changed ports on the switch...same thing, they kept dropping off of the net.
UNTIL, I changed the switch port to 100full and the servers to 100full...and the problem has not reoccured.