the first thing I would try is to reset the thumbnail cache...
http://www.tech-recipes.com/rx/4285/...umbnail-cache/
Does your pictures folder have a lot of images in it? It might be that windows has not cached all the thumbnails yet. it will do this on view (i.e., if you open the folder, then start scrolling down the page in order that it forces windows to show you a thumbnail of the image). once it has the thumbs.db full of all your images, it will be a lot faster! indexing alone does not populate the thumbs.db file.
let us know how it goes....
alternatively, use Google Picasa 3, which imo, is excellent for viewing images (and I have around 35,000 images in my library and it has no issues with speed at all)