Why not just use a regualr html link
your link
mysite.com/index.php?page=portfolio
passes the variable $portfolio as a value for the key "page" or something like that.
The you would need code to process the variable "portfolio.
for examlpe
$url = "show_book.php?isbn=".($row["isbn"]);
function do_html_url($isbn)
now the url will go to the show_book page which process the isbn, displaying the appropraite book
if you are showing a list of portfolios links on the index page
each item in the list will have a separate isbn or unique id number
then when someone clicks on the appropriate link they will be brought to the show_portfolio page where a particular item of the portfolio is shown that correponds to the isbn or unique portfolio id number. This would equal one portfolio piece per page.
then they would have to press a link to send them back to the portfolio list.
Unless of course you display all the links on your index page then post to the index page passing a variable upon which a function is run to display the appropriate portfolio piece.
If you're trying to not have your page upload each time the user clicks this may work, but I'm not sure. I know it can be done via javascript.
That leads to a new question. Can PHP do everything javascript does?
Surley you can simplify this with html.
Do you have an example site you are trying to copy?
Hope this helps