This solution does not require modifying the yui source and works on YUI version 2.5.0. It will disable the next and previous arrows based on the out of bounds dates you specify with mindate and maxdate when you configure the calendar. Requires YUI dom

1) attach an onRender event when you configure the calendar and before you call render

oCal.renderEvent.subscribe(hideOOBArrows, oCal);

2) add the following function:

function hideOOBArrows(type, args, oCal) {
	var firstDateOnNextPane = oCal.toDate(oCal.cellDates[oCal.cellDates.length-1])
	firstDateOnNextPane.setDate(firstDateOnNextPane.getDate()+1)
		
	if (oCal.isDateOOB(firstDateOnNextPane)) {
		var rightArrow = YAHOO.util.Dom.getElementsByClassName(oCal.Style.CSS_NAV_RIGHT, "a", oCal.oDomContainer)
		YAHOO.util.Dom.setStyle(rightArrow, "display", "none")
	}

	var lastDateOnNextPane = oCal.toDate(oCal.cellDates[0])
	lastDateOnNextPane.setDate(lastDateOnNextPane.getDate()-1)
		
	if (oCal.isDateOOB(lastDateOnNextPane)) {
		var leftArrow = YAHOO.util.Dom.getElementsByClassName(oCal.Style.CSS_NAV_LEFT, "a", oCal.oDomContainer)
		YAHOO.util.Dom.setStyle(leftArrow, "display", "none")
	}
}