You cannot use Verizon FiOS products at their full speed on a Windows Vista-based computer
On a computer that is running Windows Vista, you try to use the Verizon speed optimizer tool to optimize network performance. When you do this, you may notice that the Windows Vista-based computer does not achieve the Internet connection speed improvement that is achieved in Windows XP. Therefore, you cannot use Verizon FiOS products at their full speed.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB939006.