We held a first time International Festival last year. Our school is new with 145 students. It was a one day event so our approach was different than an event that lasts a whole week. However, here are some ideas.

Each classroom selected a country or culture to present. They created a booth with decorations, crafts or games and food items. Not only did the kids learn about that culture, they took so much ownership in the booth that they spent most of their time there. The American booth was stictly hot dogs, sodas and popcorn.

A big hit was passports. Each child was given a little blank booklet and the pages stamped at each booth.

If I were to do it over a week, I might emphasize different countries/continents on different days. Is this event being held during school hours? If so, you might include activities that won't wind the kids up so much, like trivia questions announced over the intercom regarding a featured culture. Answers were put in a jar in the school library and several winners were drawn each day.

EAch day the kids could dress up like the featured cultures. Maybe a bake sale after lunch of foods from a featured culture. You might include educational presentations, or guests from different cultures to present something to the students on a particular day.

Our students also learned songs with a dance from various cultures and each grade level presented their performance at our festival. The art teacher presented a student art show of their work, and the PE teacher held a contest of physical skill.
We also held a separate field day with an Olympic theme, which could be translated into games from different countries. The events were held simultaneously with classrooms of students rotating to each event at the sound of the whistle.

I don't know if these ideas are what you were looking for, but maybe they'll get your creative juices flowing.

I am a new PTO parent and our school is planning for the first time a multi-cultrual fair. We have a little over 900 students k-5th and would like to run it as a week long event. Since this is our first time we would like as much input as possible. I volunteered to be the co-chair I need help!