the view cart button code will look like:
<input name="eCart4_View_100" type="image" class="eC_ImageButton" id="eCart4_View_100" onclick="MM_goToURL('plugins/parent','');" src="WA_eCart/Images/Slate/Btn2_EN_view.gif" alt="View Cart" />
it use the javascript onclick event to go to the cart page:
onclick="MM_goToURL('plugins/parent','');"
edit the second perameter to the cart pasge name:
onclick="MM_goToURL('plugins/parent','cart.php');"