Thanks for your help, Jason.
I've implemented what you've said (and thanks for the explanation too) but it is only showing the password field as editable if it meets the "If Self" condition. I know the "Admin Priv" rule works because I'm the admin and it shows me the Group field (which is "Admin Priv") but it shows the password as a read only to me unless it's my record.
Here's my code (I have no idea why the gaps in "password" are showing up when previewing this reply. They are not in the code I've pasted):
<% If (WA_Auth_RulePasses("Admin Priv") OR WA_Auth_RulePasses("If Self")) Then ' Begin Show Region %>
<td><input type="text" class="WAATKTextField" name="txtpassword" id="txtpassword" value="<%=(rs_resident_detail.Fields.Item("txtpassword").Value)%>" size="32"/></td>
<% Else %>
<% End If ' End Show Region %>