Yes. The default logo is a GIF file (logo.gif) 350 pixels wide and 50 pixels high. If you have your own GIF logo then simply upload it as logo.gif to your server. The logo can also be a JPEG file. In that case, upload the JPEG file to the server and then change the URL to the logo in the Admin.
There is more information about changing the logo in the 'Tips and Tricks' section of this Knowledge Base.