Minecraft uses very much CPU, because it needs to loops though all the thousands of block you see in your world.
Your m-CPU isn't really that great, so it won't supprises me it lags.
As much as I agree...I play on a Intel T7500 laptop processor sometimes (centrino/core2duo) and don't lag as much as he does..so....I got nothing else to add other than that unuseful bit of info