<p>I want to add my own member to the StringBuilder class, but when I go to create it IntelliSense doesn't bring it up.</p>

<pre><code>public class myStringBuilder()
    Inherits System.Text.[StringBuilder should be here]
    ....
end class
</code></pre>

<p>Is it even possible? thanks</p>

No,
StringBuilder
is a
NotInheritable
class.  You could try wrapping a
StringBuilder
instance, but can't inherit from it.  You can also use
extension methods
, if you're using .NET 3.5.