I have a laptop (Vista) and a new desktop (Windows 7)connected to my router. The laptop, with the desktop being off, downloads at a consistent 6.7Mb/s. When I turn off the laptop and start the desktop, it downloads at a steady 1.3Mb/s.
There must be something set incorrectly on my desktop to make it d/l so slowly.
Try disabling your antivirus and then test your download. It is also possible that you have background programs that are eating up some of your bandwidth.
First: If you are not using Norton make sure to totally remove it. Disable your virus protection and test speed and if problem consist continue,
Second: Start in safemode with networking and test speed. If problem goes away then clean up desktop once out of safe mode. If not continue.
Third: Plug your laptop directely into the router and test speed. If speed is still 6.7Mb/s then you confirm your router/network cable is not the issue.
Fourth: Update bios/drivers.