It's already in the OS. Just right click the LAN activity icon in the notification area (often incorrectly called the system tray) by the clock, select properties, and there you go. Though if you're one of those people still laboring under the false notion that the reported interface speed means much of anything, allow me to tell you that it doesn't. I'll decline to teach networking basics when others have already done it far better than I could here on countless web pages, books, etc.