Xwiki Logo

Can someone explain how to change the xwiki logo in the upper left corner of the pages so that all of them will be changed? I also want to remove that gradient blue bar out of there so I can just put my company logo on it and not worry about it looking funky. Is it really as difficult as the howto on the xwiki.org site suggests or has someone developed a quick and dirty howto on this? I am new at CSS and inevitably will break something if I go messing with the skins. Peace be with all of you, Tim Suter