Generating a Thumbnail on-the-fly

I'm looking for some help. I need to know how to generate a thumbnail on the fly. Also, I was wondering, does that take an excessive amount of processing time to do? Because I'll be doing it to between 5-25 pictures at a time. Thanks for any help. - Scott

Renaming a File

Is there a function that will let you rename a file from say file.txt to file.bck? Thanks. - Scott