Here is a good tool for styling infowindows: http://google-maps-utility-library-v3.googlecode.com/svn/trunk/infobubble/examples/example.html
And some more resources at this answer: Styling Google Maps InfoWindow
Update: To put an infobubble on your map you can implement it like this, with whatever options you want below.
infoBubble = new InfoBubble({
map: map,
content: '<br><a target="_blank" href="'+place.website+'">'+place.website+'</a>',
shadowStyle: 1,
padding: 8,
backgroundColor: 'rgb(57,57,57)',
borderRadius: 4,
borderWidth: 5,
borderColor: '#2c2c2c'
});
google.maps.event.addListener(marker, 'click', function() {
if (!infoBubble.isOpen()) {
infoBubble.open(map, marker);
}
});