Yeh sorry, should have come back here and said.
We did it this way, so the field is readonly to customer and writable to Admin:
Code:
{if $usertype eq "C"}
Order Notes:
<TEXTAREA name="notes" cols="60" rows="5" readonly>{$order.notes}</TEXTAREA>
{else}
{if $usertype ne "C"}
{$lng.lbl_order_notes}:
<TEXTAREA name="notes" cols="60" rows="5">{$order.notes}</TEXTAREA>
{/if}
{/if}