Hi Medivh, and welcome to Crystal XP 
Sorry, you cannot do that with a visual style since it'll completly reapply your task bar/Start menu (not toolbar) and your windows (not OS. opening windows like my computer window, my documents window)
But you can give a try in modifying your Vista Visual style with Style Builder (shareware)
With this you can just replace the bmps of the Vista style with Vista CG and save the style as a new msstyle (visual tyle) without harming the two original Visual styles.
But this is a little complicated and should be done carefully 
If you need help just post a reply here 