The router is about 8 feet from the computer, same room. That shouldn't make too great a difference.

Last night I pulled the wireless receiver off the tower, and speed seems to increase marginally. That would seem to indicate that if both hardwire and wireless are connected, then the wireless takes precedence over the hardwire.Can this be true? Or does one just interfere with the other?

It's got to be the rest of my system, old and slow, which is causing the slowdown. Remember the fact that my daughter's laptop is significantly faster using the same cable modem.