I think I get the picture. And I stand by my original recommendation. If I understand you correctly, this is *exactly* the kind of situation the "Find a record..." combo wizard is built to address.
1) Build your form. Set the Record Source to the table or query you wish. Place your text fields on the form, but NOT the one you wish to seach on.
2) Place a combo box on the form, and select the "Find a record..." wizard. Step through the wizard, setting it up for your search field.
3) Set the combo's "Limit to List" property to "Yes" and its "Auto Expand" property to "Yes". (the wizard may do this automatically, but check it to make sure)
By using a combo instead of a textbox, you give your users the option of typing in the search value or selecting it from a drop-down list. Setting the limit to list property will prevent users from editing the data in that field: they can't add or remove items from the list, and if they type in something that's not in the list, Access will bark at them. The auto expand property will auto-fill the field as users type in the data, so they don't have to scroll down a long list to find their entry. You lose both these features (limit to list and auto expand) if you insist on a textbox for your search field. You could probably simulate those features to a certain extent with code, that's a lot harder route.
If I'm totally off base here and am misunderstanding what you are trying to do, post back with some more details.
HTH
Ken S.