Yannick seems to have it right, but here is another way

<system.webserver><rewrite><rules><rule name="DefaultRule" stopprocessing="true"><match url="^index.php"><action type="Redirect" url="/"  =""></action></match></rule></rules></rewrite></system.webserver>

No i dont think so, even if the thought they were duplicate, then they will pick one as the original. so one of them will rank.

If you are still concerned use tha canonicall tag, rather them remove them from index

If the content is different, then dont do anything, but if it is duplicate us ethe canonical tag.

The meta tages are not a problem, you are not going to get flaged for that, it would be better if you could make them unique but this is a very small problem

Thats the advice i gave you, put a canonical tag in the page

rel="canonical" href="http://www.vistastores.com/table-lamps"/>

if google finds http://www.vistastores.com/table-lamps?dir=asc&order=name

it will know it5 is mean to be http://www.vistastores.com/table-lamps

I would simplty put a rel canonical in the page point ing to the true URL. so SE's will see them as one page.

It is better to use cononical for the reasons in the google doc you posted, goolge may not pick the nest url to be the canonical, you should make that choice for them