Hi, Bec717, and welcome to allnurses!
I worked in nursing homes for many years, but not adult day care. I haven't heard of this Wii craze among the elderly, but from what I know of working in long term care it doesn't sound like it would be a very successful project. Many patients in long term care have impaired memory, can't follow directions very well, and have difficulty using their fingers for finite movement.
I would recommend that you go to a library and look at some of the articles in a geriatric journal where nurse researchers have already done some studies. Reminiscent groups and work with animals (even stuffed animals) has been more successful with the elderly. You should also talk with an Activities Director in a nursing home to get some ideas for a project as well. These people will know the patient population in their nursing home very well and should have some good suggestions for you. I have been in nursing homes where there were all kinds of activities that were done for the residents including exercise sessions, an afternoon of some of the ladies baking cookies followed by a tea party, crochet groups, parties and games, Bingo being one of the most popular, but others could also be done. Keep in mind the era that your age group of patients is coming from and what kinds of activities these men and women did. Many ladies of the 60s were primarily homemakers. The men were bread winners and depended on their wives to keep the house. They miss their old days and appreciate young people who understand their lifestyle. You will also need to work around medication and treatment schedules.
Here are some links to check out: