You would probably get a better response by using the PM (personal message) system rather than starting a new thread. It depends on what the staff think of course, but also remember outside lives are very important, and not everyone is able to get access to the internet at a whim.
Also, if this is the same banner as seen here
/forums/index.php?showtopic=1678 then all you should need to do is save the image onto your computer, and then upload it to your server area. I managed to open it myself no worries. Of course, if its a different banner, or sent to you differently, then this paragraph is useless.
I'll get to your other question, just to move things along (I hope I'm right).
Anyway, you no doubt know how to add in images using the <IMG SRC> tag. Within that tag, you simply need to specify the width (ie: WIDTH=%) that way is the best, because then you can set the width to be a percentage of the person's screen. If you use pixels, then its possible the images will bee too long for someone whos resolution is only 640x480, or look too small on someones screen with a large resolution (whatever they are)
So, to stretch it all the way across, it would be set to 100%. Take note, stretching the image so much will likely warp it because the vertical size will remain the same.
For example <IMG SRC ="http://www.your_pic_here.jpg" WIDTH=95%></IMG>
That's about it - I think