I was wondering if it was possible to make snowballs deal damage to players and mobs, using command blocks?
I'm playing Minecraft 1.7.10
I think not, but in 1.8 you can beacause of replace. Detect if a player is in 0.1 block range of the player, then replace the snowball with an arrow or other things. You can do cool things like detect if a snowball is in range of a gold block, put a diamond on the gold block, or you could do this but with an egg that has an 0% chance of hatching a chicken.
Anyway, you can do some similar but cooler things using bukkit. either update to 1.8(out now) or use bukkit. I recommend using bukkit.