You can change the start orb without changing the theme or msstyle.
1. You need to have vista style builder 2. Open the msstyle file with vista style builder 3. on the left panel, click Start--> Start Button-->Middle 4. On the right panel select Import (you need to have png file containing 3 orbs for different orientations of start button) 5. Repeat step 4 for Bottom and Top options under Start Button 6. You can test the msstyle by clicking test button on the top 7. Save the msstyle with what ever name you want and apply the msstyle to get your original theme with start button of your choice