How did you discover these files may I ask? Are they causing any problems? Until I saw your post I hadn't heard of that file extension before.
I've around 960 .pnf files, most of which are in the C:/Windows/inf folder with a combined size of about 34Mb (which isn't 'enormous' as I have 2x 80Gb hard drives).
If you're running out of space backup them up to removable media just in case. Otherwise, leave them alone. G