for this achievement you must have someone on your xbox friends list that has played this game. they only have to have started it up. i just installed the game on my daughter's profile, started the game, let it load up, and didn't even do the first step of the tutorial. i just exited her back out right away. if you want to, feel free to add me ( QuickMythril ) to your friends list. you might as well send me a gift when you can and i will be sure to send it back.
the actual process is to click on the little People icon, and on the People tab, press the Airplane icon next to their name. the Gift icon will send a present, but is only available once every 24 hours. after your friend's zoo loads, you can immediately click the Home icon in the lower left. once you get back to your zoo, go back and visit them again. after 100 visits this achievement should unlock.
also after about every 4 visits your concession stands should be missing 1 stock, so i restocked between visiting. that way i would have restocked 25 times by the time i reached 100 visits. there is an achievement for restocking concessions 500 times, which seems like it might take a while so i figured every little bit extra helps: