Yes. During the automated upgrade from version 4 to version 5, your template will be automatically converted to a version 5 template. After the upgrade the site will look and function exactly as it currently does. Being in the new template format though makes it much easier to take full control of the look and feel of your website using the tools you or your designer are comfortable with (e.g. DreamWeaver).
If you prefer, it will be possible to switch to one of our new standard templates and use it as is, or use it as the basis for a new design.