Setting Custom Fields

I have setup a custom field called Name that is a drop down list.  I would like the user to be able to select a name from a drop down list that displays clients already setup in the client list (instead of manually loading the options and/or uploading a client list.  I may want to do something similar for other custom fields, as well as load additional info about the client from the selected client's profile.  Is this possible?  If so, how?

Thanks

Steve