[maxhodges]

You should alter the "<xart_dir>/skin1/modules/News_Management/register_newslists.tpl" template.

Find this code:
<input type="checkbox" name="subscription[{$listid}]" {if $subscription[$listid] ne ""}checked="checked"{/if} />

And replace it with this:
<input type="checkbox" name="subscription[{$listid}]" {if $subscription[$listid] ne "" or $login eq ""}checked="checked"{/if} />