Link speed effect

HI all,

i am working as a network engineer At Grand Hyatt Amsterdam.Basically the guests connect to the net using the wired connection.My question is when the link speed settingof the LAN card is Auto detect or 100 mbps the internet browsing is slow.However on converting the link speed to 10 mbps 1/2 duplex the speed of browsing increases.
Hows that so when i am actually reducing the speed