Windows Vista does not use all the bandwidth of a PPPoE connection when you download a file from an FTP server
On a Windows Vista-based or Windows Server 2008-based computer, you try to download a file from an FTP server through a 100 Mbps Point-to-Point Protocol over Ethernet (PPPoE) connection. However, only 30% network bandwidth is used. In this case, the file download speed is limited to 30 megabits per second (Mbps).
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB960519.