Access Field Variables within Edit Record

Hi,
In the visual editor for the Edit screen I placed a hyperlink within a cell that calls a php script -
<TD width=111>&nbsp;<A href="gen_contract.php"

target=_blank>Generate Contract</A></TD>
which works fine but what I really want to do is pass the Key Value of the current record e.g.
<TD width=111>&nbsp;<A href="gen_contract?ncaf_id=KEYVALUEOFRECORD"

target=_blank>Generate Contract</A></TD>
What is the best way of going about this.
Thanks,

JP.