In the table of contents page of the frame version I was able to create a
drop down list for selecting from various categories of products. 
Code as follows:-
 
<FORM METHOD = "post" TARGET="main" ACTION = "./web_store.pl">
<INPUT TYPE = "hidden" NAME = "cart_id" VALUE = "%%cart_id%%">
<TABLE BORDER=0>
<TR><TD><INPUT TYPE = "image" VALUE = "go" SRC="./images/go.gif"
border="1"></TD>
        <TD><SELECT NAME="page">
        <OPTION VALUE="categorie1.htm|&cart_id=">Categorie 1
        <OPTION VALUE="categorie2.htm|&cart_id=">Categorie 2
        <OPTION VALUE="categorie3.htm|&cart_id=">Categorie 3
        <OPTION VALUE="categorie4.htm|&cart_id=">Categorie 4
</SELECT><BR></TD></TR>
</CENTER>
</TABLE>
</FORM>