Hi -
I just changed the logo on our new installation today. It was super easy:
just uploaded the new logo to the templates/default/images/ directory and then just went into each of the templates, like home.html and changed the code on line 17 - 18.
It should look something like this, except the new file I modifed has a slightly different name than the original, and its still a gif unlike your .jpg but that shouldn't make a difference:
<td width="6"><img src="{template_url}/images/header_left.gif" width="6" height="60" alt="" /></td>
<td width="100%"><img src="{template_url}/images/glrfheader_logo.gif" width="405" height="60" alt="" /></td>
Had to go through and do the same modification to about 8 templates.
- Brian