How is bursting accomplished? Can it be done without GS?

yes.. u can burst with no gs.. but naturally u'll get less exp then with it ^^
u just need to use your debuff skills.. and a team that does lots of dmg =P

bursting is accomplished by having a group with 2 or 3 buff/debuff spell casters. You have 1 fighter, high level, and all 4 players have a lvl 1 pet. The fighter needs speed 0 so they can combo attack witht he low level pets. For the 1st 2 rounds the fighter and the pets all block while the buff/debuff players cast those spells. Those spells add a EXP bonus multiplier, so casting as many of them as you can really helps. Now on the last round, the pets and the fighter all attack. The goal is for all the pets and the fighter to attack in 1 big combo and have the highest speed of those attacking be one of the low level pets. This will create a big combo, that does alot of damage because of the fighter and is seen by the game to be a combo thats lead by a low level pet. When the game see's that a low level pet killed a fairly higher level mob and did alot more damage than expected, due to the fighter being part of that attack, the game then assigns a good amount of experiance to that attack. Then from the buffs/debuffs, the EXP gets multiplied.

exactly