Show but hide out of stock products

[gmrm]

I have a question, i want the customer to be able to choose whether to show out of stock items or not. Here is an example (i know this is not a zen cart site) :-

http://www.chilloutgames.co.uk/Gameb...boy_Games.aspx

there is a tick box to show/hide out of stock products. This would be really nice feature for google indexing :) so people would still find my site.

How would i be able to add this to zen cart. Is there any way ??

Please help and many thanks

[gmrm]

I have installed the StockFilter contribution but its not working on 1.3.8h

[gmrm]

i have sort of got it working, but if i add the code to the categories i get a blank page. Also i am very worried about duplicate content as this adds www.gloopy .co. uk/index/stock_filter/in_stock to the page so would google not index that