If you turn off the wireless and turn down the screen brightness, you could get 3 hours with a new unit. How long the battery will last with a used unit is hard to say. As far as putting the 80Gb notebook hard drive in, that shouldn't be a problem provided they share a similar connector. Most tablets just require two screws to open a panel on the back - I don't have that info on the 4110.
As far as RAM, you can get the info and purchase here: