Are you looking for assistance with creating your own graphic, or do you need help with actually changing the logo?
We do have a graphics forum here, if it's the former.
If it's the latter, then you can actually just do this from your control panel. First use FTP to upload your custom images to the NonCGI directory you created at installation. This is the directory where the UBB graphics and HTML files already are stored. All custom graphics must go in this folder. If you decide to change the image name in this section, enter only the filename (i.e. newgraphic.gif) not the full URL to the graphic.
Then go into your Style Settings and switch the graphic to the new one.