You can do things like:
<%if Tag eq 'x'%>selected<%endif%>
for select lists and
<%if Tag eq 'x'%>checked<%endif%>
...for check boxes, where x is the value
<%if Tag eq 'x'%>selected<%endif%>
for select lists and
<%if Tag eq 'x'%>checked<%endif%>
...for check boxes, where x is the value