If someone kills you in Diablo 2 can they take all your items?
No, no one can loot your body for items in Diablo 2 PvP. When you die, you drop an item called an "ear" that is just proof that someone has killed you, and you drop all of your gold that is currently on your character and not in your stash.
If you are in hardcore mode and you choose to allow the to loot your corpse (little padlock-symbol in party screen) then they can take the items you were wearing (however not those inside your inventory or stash).
However this means that they can't just kill you over and over on the same character given the fact that in hardcore characters are gone once they died.