$(document).ready(function(){
    var pageCounter={//页面记数器
            pages:1,
            currentPage:1,
            getPageUp:function(){//获得上一页
                var _pageUp=this.currentPage-1;
                if(_pageUp<1){
                    _pageUp=this.pages;
                    }
                return _pageUp;
                },
            getPageDown:function(){//获得上一页
                var _pageDown=this.currentPage+1;
                if(_pageDown>this.pages){
                    _pageDown=1;
                    }
                return _pageDown;
                },
            pageUp:function(){//向上翻页
                var _prePage=this.getPageUp();
                this.currentPage=_prePage;
                },
            pageDown:function(){//向下翻页
                var _nextPage=this.pageDown();
                this.currentPage=_nextPage;
                }
        };
    //initPpt();//初始化
    pageCounter.pages=5;
    var pptSwitch=function(){
                //$('#bgImgPPT').find('img').eq(pageCounter.currentPage).animate({'top':'0px'},2500).fadeOut(250);
                pageCounter.pageDown();
                alert(pageCounter.currentPage);
                //$('#bgImgPPT').find('img').eq(pageCounter.currentPage).fadeIn(250).animate({'top':'0px'},2500);
        }
    var ppt=setInterval(function(){pptSwitch()},3000);
    });

            pageDown:function(){//向下翻页
                var _nextPage=this.pageDown();
                this.currentPage=_nextPage;
                }

------解决方案--------------------
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JScript code
            pageDown:function(){//向下翻页
                var _nextPage=this.pageDown();
                this.currentPage=_nextPage;
                }

没看错吧，pageDown无限调用自己？
var _nextPage……