I'm not sure if you can alter the access find parameters but you can set up the same on your own form. Set up an unbound textbox eg txtSearchText and add a button to the form (without the wizard)
on the onclick event of the button
set the code to the following
Dim strCriteria as string
strCriteria = me.txtSearchText
docmd.findrecord strCriteria, acAnywhere, , , , acAll
this will search all fields for the string you typed into the box in any part of any field. Have a look in help for FindRecord to explain the syntax and how you can play with it.
HTH