explorer.exe being an absolute memory hog

Hi there, I can use my PC like normal, opening and closing programs, but as
soon as I browse using My Computer or Windows Explorer to a folder that
contains images, explorer.exe goes though the roof with the memory usage.
Shoots from 25k to over 100mb in no time. Even saw it go over 1gb yesterday.
I have virus scanned repeatedly, scanned for spyware, run hijack this, and
the computer looks completely clean. Also, I dont know if this is related or
not, but the thumbnails of the pictures are alot smaller than normal, and
some of them look like the are in 256 colors not the usual 32 bit. I'm
stumped on this one, hopefully someone can point me in a direction I should
be looking. I've googled my butt off looking for an answer, but thus far, to
no avail. Cheers