When you're in folder view, how can you view actual thumbnails, and not just program icons?

I asked a similar question before, but I'm not sure if the person who answered read it properly, or if I was being clear, because I never got the right answer, so I'm trying one more time.

When you are in a folder looking at images on a Windows computer there is an option to view them as thumbnails. Now my problem is that when I was using Windows XP I had no problem, and they would show me the actual thumbnail. But when I switched to Windows Vista, when I went to view thumbnails all it would do is show a bigger icon of the irfanview icon (irfanview is the default program I view my images with). So please don't suggest right clicking and view then thumbnails.

So what I'm asking is, is there a way to view thumbnails of my images in the folder view instead of just the irfanview icon.

It would be greatly appreciated, because I use a lot of textures that have somewhat ambiguous names (eg: metal001, metal002...) so I can't just go from what the name is and guess. I have hundreds of images to search through to find the right one, and that takes forever, so seeing a thumbnail would just make my life so much easier.

I do have Picasa which would in theory at least help, but the problem is I'm also a bit of a photographer, and have literally thousands of other photos on there, so it also wastes time to find where my textures are on that.

Not sure if you need to know, but I'm running Windows Vista 64bit computer.