Must use a bow and upgrade it to +3 through regular means before you can start using Spiderstone. You have to take to the blacksmith Ed in 2-1 to finish upgrading to +5. If you don't know where to Spiderstone use this to help you by.
Shards: Kill the Lizard men in 2-1 & 2-2.
Chunk: Found as a treasure in the arena that you fight Armor Spider (2-1).
Pure: Awarded after you defeat the Armor Spider (2-1) boss.
Credit to: (http://psnprofiles.com/guide/989-Demons-Souls-Trophy-Guide#M...