They are coded as buttons:
<asp:button id="cmdLogin" resourcekey="cmdLogin" cssclass="StandardButton" text="Login" runat="server" width="100%" />

BUT you can style them to almost look like text links by setting the StandardButton class in your skin.css file:
.StandardButton {
background: #ffffff none;
border: 0px;
color: black;
text-decoration: underline;
font-family: Arial, Helvetica, sans-serif;
font-size: 11px;
font-weight: normal;
}
Adjust the colors, font, etc. to match your skin.  I wasn't able to set a different style for hover, etc...