Posting here is OK but it would have been better placed in Mod Pack Bugs.
Do the following:
Download the most recent 1.4.7 version of Minecraft Comes Alive since the 1.5.1 version will not work
click on the Force Update in the Options Tab in the launcher up the top and run Magic World. This will make the pack as if you just downloaded it
quit out of the game and load up the launcher again.
click once on magic world and dont launch it
click on edit modpack and click add mods
find where you downloaded the minecraft comes alive version and add it in
close that tab and run the modpack, it should run fine but if it gets a crash log make sure to post it here and we can help.