The textboxes have the .NormalTextBox class applied, and they are inside of a div with the .LoginPanel class.  So, you should be able to define a style in your skin.css like so:

.LoginPanel .NormalTextBox {
  width: 150px;
}

Hope it helps,

Ah, I hadn't noticed that.  Same on the text boxes.  You'll need to override those with an !important directive, like so:

.LoginPanel table {
  width: 450px !important;
}

.LoginPanel .NormalTextBox
{
    width: 450px !important;
}

Hope it helps,