associate a hidden input to (chosen) select option in form?



<form action="http://www.mmmm.org/cgi-bin/search"; method="get">
<input name="yyyyyy" value="1" type="hidden">
<input name="query" size="50" value="">
<select name="zzzzzz">
<option value="888">YOU-WANT-THIS</option>
<option value="899" selected="selected">OR-KEEP-THIS</option>
<option value="999">OR-CHOOSE-THIS</option>
</select>
</form>

i'd like
to convert input name="yyyyyy" to a select name="yyyyyyy" (or whatever that can have
more than one value assigned) that is
1 also chosen when user chooses the select name="zzzzzz" option.
2 still hidden (this isn't terribly important, though)

so this
<input name="yyyyyy" value="1" type="hidden">

would instead look something like
<select name="yyyyyy">
<option value="1">1 but you can't see this</option>
<option value="2">2 but you can't see this</option>
<option value="3">3 but you can't see this</option>
</select>

except it would actually look like whatever would work :-)

unless this is impossible? or possible only with script?

------
googling the likes of
http://groups.google.com/groups?q=select+name+options+%7Etied+form+html
associated multiple two-options
gave optgroup or less likely answers

tia...
.