I have the field on a form with instructions to right click and insert object. Is there a better way of showing this on a form and thus adding validation rules?
Yes I would do this through a form. Here is some excellent code for how to have the user browse to a file: http://www.mvps.org/access/api/api0001.htm
Look carefully at the code and you will be able to figure out how to only show them zip files. Then, after they have selected a file, get the file name, and check right(filename,3) to see if it equals "zip". If it doesn't, you can warn them to try again and pick a zip file.