These instructions apply to the default skin, Confluence.
First you need to find the directory containing whatever skin you're using. I don't know where XBMCbuntu keeps the skin files: in Windows the default skin is in "C:\Program Files (x86)\XBMC\addons\skin.confluence\720p".
Anyhow, you need to find the file called Home.xml. Open this file in your favourite text editor and go to line 603. The two lines 603 and 604 look like:
Code:
<onclick condition="!Skin.HasSetting(HomeVideostoFiles)">ActivateWindow(Videos)</onclick>
<onclick condition="Skin.HasSetting(HomeVideostoFiles)">ActivateWindow(Videos,Files,Return)</onclick>
You need to replace these two lines with:
Code:
<!--
<onclick condition="!Skin.HasSetting(HomeVideostoFiles)">ActivateWindow(Videos)</onclick>
<onclick condition="Skin.HasSetting(HomeVideostoFiles)">ActivateWindow(Videos,Files,Return)</onclick>
-->
<onclick">ActivateWindow(Videos,<directory name>,Return)</onclick>
Where <directory name> is the name of the directory you want to open. If you're using XBMCbuntu you've probably got the files on a network server, in which case <directory name> will be something like "smb://server/share/whatever/".
Note that in the code above I haven't deleted the lines originally in Home.xml, I've just commented them out. This makes it easy to put Home.xml back to what it was if you ever change your mind. You should also take a backup of the file so you can restore it if something goes horribly wrong.