Any wordpress guru around here?

[Sonic]

General:
img {
max-width: 580px;
height: auto;
}

By class:

.thumbnails {
max-width: 120px;
height: 120px; /* You can set it auto */
padding: 10px; /* to add 10px space on top, right, bottom, left */
}

usage: <img class="thumbnails" src="myphoto.jpg">