Here is the full list of all 19 Assassin's Creed: Altaïr's Chronicles HD achievements worth 200 gamerscore.
Kill 5 enemies using a Crossbow
Complete Memory block 7
Perform triple jump
Sword maximum upgrade
Kill 5 enemies using an explosive bomb
Kill 5 enemies by throwing daggers
Complete Memory block 4
Complete Memory block 3
Kill 5 enemies using a Finger Blade
Complete Memory block 2
Complete Memory block 1
Kill all enemies in level 1
Kill an enemy instantly using a Finger Blade
Kill 1 enemy
Perform all combos
Complete Memory block 9
Complete Memory block 12
Complete the game
Complete level 13 without losing any hit points