In forum.asp, look for this code or something similar. this is from 3.3, but should be the same in 3.1
if nDays > "0" then
strSql = strSql & " AND " & strActivePrefix & "TOPICS.T_LAST_POST > '" & defDate & "'"
end if
change it as follows.
if nDays > "0" then
strSql = strSql & " AND (" & strActivePrefix & "TOPICS.T_LAST_POST > '" & defDate & "'"
strSql = strSql & " OR " & strActivePrefix & "TOPICS.T_INPLACE = 1 )"
end if
Not tested this, but it sould meaan that it always selects locked in place topics regardless of date.