As Srik commented, use a different panel like this for example :
function test(){
showURL('Google','http://www.google.com','Stackoverflow','http://stackoverflow.com/questions/tagged/google-apps-script')
}
function showURL(name1,href1,name2,href2){ // for ease of use I give the urls as parameters but you could define these urls in the function as well
var app = UiApp.createApplication().setHeight(60).setWidth(200);
app.setTitle("Show URLs");
var link1 = app.createAnchor(name1, href1);
var link2 = app.createAnchor(name2, href2);
app.add(app.createVerticalPanel().add(link1).add(link2)); // add others as needed
var doc = SpreadsheetApp.getActive();
doc.show(app);
}

EDIT : thanks for accepting - if you need it to be dynamic try something like this, using an array as argument :
function test(){
showURL(['Google','http://www.google.com','Stackoverflow','http://stackoverflow.com/questions/tagged/google-apps-script','Google','http://www.google.com','Stackoverflow','http://stackoverflow.com/questions/tagged/google-apps-script'])
}
function showURL(data){ // for ease of use I give the urls as parameters but you could define these urls in the function as well
var app = UiApp.createApplication().setHeight(40+8*data.length).setWidth(200);
app.setTitle("Show URLs");
var panel = app.createVerticalPanel();
app.add(panel);
for(var d=0 ; d<data.length;d=d+2){
var link = app.createAnchor(data[d], data[(d+1)]);
panel.add(link);
}
var doc = SpreadsheetApp.getActive();
doc.show(app);
}