Attempting to get SP 2010 to display PDF icon in doc libraries

So we are having a couple of odd image related items on our new SP 2010 farm.

It first showed up when the icon for PDFs that users were seeing was not the familar PDF icon they see on our old SP 2007 farm.

Then users reported that the company logo on many SP 2007 pages was instead showing up as a Microsoft logo.

It turns out both of these were images that had been placed in the 12hive TEMPLATE/IMAGES folder.

So I copied the files over to the 14hive TEMPLATE/IMAGES folder.

I even did an iisreset just to be certain that there was no cache problem.

However, the images displayed on the SP 2010 farm are still the old ones that should have been replaced or updated.

What other things do I need to do so that this works?

Thank you!