[josh_krz]

I'm not sure if you can do this with vB options but you can use CSS.

I don't understand about the stretching problem. There would be no other way of achieving this without stretching. However if you mean you would like to keep the images aspect ratio then you can use:

.postuseravatarlink img {
max-width: 30px;
}

This should keep your aspect ratios but it won't scale up images, only shrink them. This way all images look good and nothings pixelated.

However if you would still like to scale images up you can use:

.postuseravatarlink img {
width: 30px;
}

Notice how I am leaving out the height in both examples? Browsers tend to automatically scale images proportionally when the height is not defined.

Here is a JSfiddle you can use to try this out:
http://jsfiddle.net/AUft5/1/