Silverstripe Tip of the Week:
If you want to open a “Other website URL” Link of a RedirectorPage in a new window with target=_blank, you can use the following snippet:
<% if ExternalURL %> <a href="$ExternalURL" class="external" target="_blank">$MenuTitle.XML</a> <% else %> <a href="$Link">$MenuTitle.XML</a> <% end_if %>
Edit:
Or this one:
<% if is_a(RedirectorPage) %><% if RedirectionType = External %>target="_blank"<% end_if %><% end_if %>
found here: http://www.silverstripe.org/general-questions/show/9600
Hope it Helps!