The answer is in the rulings at the bottom of the page inside the Gatherer entry for Talrand, Sky Summoner
7/1/2012 You'll put the Drake token onto the battlefield before the spell that caused the ability to trigger resolves. However, that Drake token isn't on the battlefield when you choose targets for that spell.
7/1/2012 The ability will still resolve if the instant or sorcery spell gets countered.
If you want to know why this is the case, you need to understand the fundamental feature of resolving spells and abilities in MtG, the stack. The stack is a First In Last Out (FILO) zone where spells and abilities go while they are waiting to be resolved. Since triggered abilities can occur at any time, the rules need a way of handling the Timing and Prioriy for placing triggered abilities on the stack, as well as handling casting spells and activating abilities. Talrand, Sky Summoner's ability triggers in the middle of casting a spell (Massive Raid in this case), which requires completing all steps from 601.2a-g. This includes paying costs, choosing targets, and other things. Only after performing all those steps is the spell considered cast, then the next time you recieve priority, you place the "put a token on the battlefield" on the top of the stack.
When all players pass in succession, the top object on the stack resolves. So, the token is created first, before Massive Raid resolves and deals damage. It will count all your creatures on the battlefield when it resolves to determine the amount of damage, which will include the token (unless an effect destroys that token before Massive Raid resolves)
601.2h Once the steps described in 601.2a–g are completed, the spell becomes cast. Any abilities that trigger when a spell is cast or put onto the stack trigger at this time. If the spell's controller had priority before casting it, he or she gets priority.
116.2a Triggered abilities can trigger at any time, including while a spell is being cast, an ability is being activated, or a spell or ability is resolving. (See rule 603, "Handling Triggered Abilities.") However, nothing actually happens at the time an ability triggers. Each time a player would receive priority, each ability that has triggered but hasn't yet been put on the stack is put on the stack. See rule 116.5.
603.3. Once an ability has triggered, its controller puts it on the stack as an object that's not a card the next time a player would receive priority. See rule 116, "Timing and Priority." The ability becomes the topmost object on the stack. It has the text of the ability that created it, and no other characteristics. It remains on the stack until it's countered, it resolves, a rule causes it to be removed from the stack, or an effect moves it elsewhere.