Ext.onReady(function(){
     Ext.BLANK_IMAAGE_URL ='../ext/resources/images/default/s.gif';
     Ext.QuickTips.init();
     Ext.form.Field.prototype.msgTarget = 'side';
     var p = new Ext.Panel({
        title: 'My Panel',
        collapsible:true,
        renderTo: 'User_InfoMange',
        width:400,
        html:'<font color=blue>asdflkj<br/> aslkdfj <br/>lkajs lkfj<br/> alskdj f<br/></font>',
        buttonsAlgin:'center',
    //    config:{
    //        buttonsAlgin:'center'
    //    },
        tbar:[
        ]
    });
    for(var i=0;i<50;i++){
        p.getTopToolbar().add(new Ext.Toolbar.Spacer());
    }
    
    p.getTopToolbar().add({text:"显示"});   
    
});

------解决方案--------------------
试试这个，关键就在于'->'，这是tbar里是按钮居右的符号，就像'-'是分隔符一样。
JScript code

tbar:[{
            xtype:"label",
            text:"管理员："
        },{
            xtype:"label",
            text:Cookies.get("LogName")
        },'->',{
            xtype:"tbbutton",
            id:"button_password",
            text:"password",
            handler:function(){
                if(!win_password)
                {
                    win_password = CreateWindow({
                        el:"win_password",
                        title:"修改密码",
                        items:CreateFormPanel(form_passwordConfig)                                          
                    });
                }
                win_password.show("button_password");
            }
        },'-',{
            xtype:"tbbutton",
            id:"button_reg",
            text:"register",
            handler:function(){
                if(!win_reg)
                {
                    win_reg = CreateWindow({
                        el:"win_reg",
                        title:"修改密码",
                        items:CreateFormPanel(form_regConfig)                                          
                    });
                }
                win_reg.show("button_reg");
            }
        },'-',{
            xtype:"tbbutton",
            text:"logout",
            handler:function(){
                Ext.MessageBox.confirm("警告","您确定要注销吗？",function(button){
                    if(button == "yes")
                    {
                        window.location = "../Default.aspx";
                    }
                });
            }
        }]