In the AfterUpdate event of the checkbox, you'd use something like:
If Me!chkMyCheckbox = True Then
Me!txtMyParticularTextControl = 1
Else
Me!txtMyParticularTextControl = 2
End If
If you want to input a value instead of using the "canned" value "2", check
Access HELP for the Input() function.

Signature
Good luck
Jeff Boyce
<Access MVP>
> In a form how can i get a particular field to equal '1' only when a check box
> is true?? If the check box is not true - can I enter a specific value or
> will it have to equal a set value?