Please check with the archive. I think somebody asked
that question sometimes at the beginning of the week.

use a software ACDSee32, that can help you in
converting a bmp  into many other file format. Also it
can help you in changing the file size(thumbnail is
actually a small sixe image  od the original)

You can genenrate thumbnails using some simple toolkits directle instead of resizing them:
www.yiigo.com/.../how-to-create-thumbnail.shtml