Rick,
Not sure if you're looking for a programmatic way to change the timestamp. If not, check the tool BeyondCompare from http://www.scootersoftware.com. This is one of the best utilities I've come accross. An excellent directory and file comparison tool. One of the features it offers is "touch" which allows you to synchronize timestamps of files in different directories, set the timestamp to the current time or change it manually.

Hope this helps,
Daniel