I might be groping in dark, but this is one of those area of Selenium1 where you could do trial and error.
Try these methods and see if any one of these gets you through -
void mouseDown(java.lang.String locator)
Simulates a user pressing the left mouse button (without releasing it yet) on the specified element.
void mouseDownAt(java.lang.String locator, java.lang.String coordString)
Simulates a user pressing the left mouse button (without releasing it yet) at the specified location.
void mouseDownRight(java.lang.String locator)
Simulates a user pressing the right mouse button (without releasing it yet) on the specified element.
void mouseDownRightAt(java.lang.String locator, java.lang.String coordString)
Simulates a user pressing the right mouse button (without releasing it yet) at the specified location.
void mouseMove(java.lang.String locator)
Simulates a user pressing the mouse button (without releasing it yet) on the specified element.
void mouseMoveAt(java.lang.String locator, java.lang.String coordString)
Simulates a user pressing the mouse button (without releasing it yet) on the specified element.
void mouseOut(java.lang.String locator)
Simulates a user moving the mouse pointer away from the specified element.
void mouseOver(java.lang.String locator)
Simulates a user hovering a mouse over the specified element.
void mouseUp(java.lang.String locator)
Simulates the event that occurs when the user releases the mouse button (i.e., stops holding the button down) on the
specified element.
void mouseUpAt(java.lang.String locator, java.lang.String coordString)
Simulates the event that occurs when the user releases the mouse button (i.e., stops holding the button down) at the specified location.
void mouseUpRight(java.lang.String locator)
Simulates the event that occurs when the user releases the right mouse button (i.e., stops holding the button down) on the specified element.
void mouseUpRightAt(java.lang.String locator, java.lang.String coordString)
Simulates the event that occurs when the user releases the right mouse button (i.e., stops holding the button down) at the specified location.
~ seleniumtests.com