You can make a theme, and override the sidepanel() function in qa-theme.php.
function sidepanel()
{
$this->output('<div class="qa-sidepanel">');
$this->output('<br><br>');
$this->search();
$this->output('<br><br>');
$this->output('<br><div style="background:url('.$this->rooturl.'welcome1.png) no-repeat;width:176px;height:72px;"></div>');
$this->output('<br><a href="/about"><img title="About" src="'.$this->rooturl.'welcome2.png"></a>');
$this->output('<br><div style="background:url('.$this->rooturl.'welcome3.png) no-repeat;width:176px;height:136px;"></div>');
$this->output('<br><a href="/ask"><img title="New thread" src="'.$this->rooturl.'welcome4.png"></a>');
$this->widgets('side', 'top');
$this->sidebar();
$this->widgets('side', 'high');
$this->nav('cat', 1);
$this->widgets('side', 'low');
$this->output_raw(@$this->content['sidepanel']);
$this->feed();
$this->widgets('side', 'bottom');
$this->output('</div>', '');
}