[Leica] Leica Communities - Help needed

[George Huczek <ghuczek@sk.sympatico.ca>]

Someone please help me off list with this. Email privately.  No need to
bore everyone with a question from a digital neophyte.

I tried to post a photo in Leica Communities.  It is the last one, under
Class of 00.

The photo came out HUGE!  How do I get it to come out smaller?  I scanned a
4x5 B&W print on a flatbed scanner.  That, in itself was an experience!  I
used 300 dpi and saved the image as a JPG file.  I fiddled with brightness,
contrast, and gamma, but lost lots of detail in the highlights and shadows.  

Anyway, the problem is that when you select the thumbnail image on the
Leica Communities website, the image gets blown way up and it looks awful.

I need to know - is jpg the best format to use?
      - how do I "size" the image that is loaded so that it doesn't come
out so large.
      - how do I retain image tonality with a flatbed scanner? I'm using a
Microtek scanner, with Microsoft Photo Editor.