i can suggest you to go this way:
find where in the template you have the link to the archive,
then replace it with code that does
if USER then LINK
else alert("you need to be logged in to get to this")
that may be hard to get if you are not good at editing
I'm not a good editor, but here a code to link
<td class="quickCol">
<div class="quickBtn {.if not|{.get|can access.}|disabled.}"><a href="%item-url%"><img src="/template/{.!theme.}/images/go.gif" alt="GO"/></a></div>
{.if|{.get|can archive.}|<div class="quickBtn1 {.if not|{.get|can access.}|disabled.} "><a href="%item-url%~folder.tar{.if|{.get|can recur.}|?recursive.}" title="{.!lv_archiveTitle.}">
<img src="/template/{.!theme.}/images/download.gif" alt="DL"/></a></div>|<div class="quickBtn1 disabled"><img src="/template/{.!theme.}/images/download.gif" alt="DL"/></div>.}
</td>
</tr>
Any suggestion ?
If not, sorry to bother you ...