Hi
You can customize the TinyMCE buttons using the HtmlEditorConfig class. To add image and link buttons, add the following to mysite/_config.php
HtmlEditorConfig::get('cms')->addButtonsToLine(1, 'ssimage', 'sslink', 'unlink');
You can also completely customize the buttons in the editor, by using ->setButtonsForLine( <lineNr>, <buttonA>, <buttonB>, ...);. For more information, I suggest you have a look at the HtmlEditorConfig class (sapphire/forms/HtmlEditorConfig.php)
An overview of the available TinyMCE controls can be found here: http://wiki.moxiecode.com/index.php/TinyMCE:Control_reference
Above I added 'ssimage' and 'sslink' (instead of 'image' and 'link') which are SilverStripe specific extensions. Sadly, I don't know where and if these are documented.