Add a field to your links database (lets call it premium), where default value could be 0 for normal entries and 1 could be the value for premium entries. Than you have to build into category.html something like this:

<%if links%>
<%if premium eq 1%>
<%links%>
______________________ (your choice of divide)
<%endif%>

<%if premium eq 0%>
<%links%>
<%endif%>
<%endif%>

If this doesn't work, play around a little bit with the <%if ...%> tags, it's pretty easy (more is explaned in Help).

Regards,
Andy