[pauldodman]

Firstly, you need to find the id of the product - the productid - you can find this by seeing what the link is in a browser.

Then open up skin1/customer/main/products.tpl

find:
{include file="customer/main/buy_now.tpl" product=$products[product]}

And then you need to put an if statement around this code.

{if $products[product].productid ne "xxx"}
{include file="customer/main/buy_now.tpl" product=$products[product]}
{/if}

obviously swap xxx for the product id no.

this will then only show the buy now button if the product is not that one.