Cacher is the code snippet organizer for pro developers

reference:
http://stackoverflow.com/questions/6871611/directly-go-to-product-detail-page-on-click-of-a-category-in-the-nav-bar



In Magento Admin:

1) Select from menu bar Catalog > URL Rewrite Management.
2) Click on the Add URLRewrite button.
3) Select the category you want to redirect from.
4) Make a note of the ID Path (e.g.: category/10) and the Request Path (e.g.: flowerpots.html)
5) Repeat steps 1 & 2, but this time select Custom from the Create Urlrewrite dropdown box.
6) Enter the values in each field:

ID Path (from step 4)
Request Path (from step 4)
Target Path - enter path of your product (or the page you want to redirect to).
example 1: for product url www.myswebsite.co.uk/flowers.html enter flowers.html.
example 2: for product url www.myswebsite.co.uk/sale/garden/flowers.html enter sale/garden/flowers.html.

7) Select Redirect Permanent (301) from the Redirect dropdown.

8) Save.
Now when the category is clicked on on your website it will re-direct to the product.