Windows – Wireless slow, but very odd

A) check that your computer has a proper IP for your network (if your working laptop gets something on 192.168.x.x then so should the other)

B) check that you don't have a proxy configured for your web browser.

C) check that you can ping your router from the non-browsing laptop.

I'd focus on first getting the wired connection working first to simplify your troubleshooting. Don't worry about the wireless until you get wired working.

I would guess that you are facing a problem of wireless interference, so that lowering the packet length minimizes the damage done by lost packets and the time it takes to resend the packet.

If the problem is interference exterior to your home, you could use a wireless network detector to detect the networks around you and the channels that are used. Some such products are inSSIDer or Kismet. You could then choose a channel that doesn't conflict with your neighbors. Channel 11 should be preferred, if possible, as it is the strongest.

The interference may also be caused by a heavy home appliance working (such as the dish-washer), at your place or at the neighbor's. This only applies if the effective network speed undergoes fluctuations.

The placement of the wireless router is very important. It should be positioned away from metallic or electrical elements and away from the floor. You could experiment with various places for it to see if this has any effect. The computers using it should not be placed too far away or at the end of its range.

Another possibility is that some wireless network card in your house is defective and deranges the entire network. It could be "bombarding" the network with packets and causing collisions. Try to turn on computers in a controlled manner and test network speed (turning them off by also unplugging the power cord).

Last, you wireless router may be defective. Try another router to test it out.