OK, I figured out how to show a preview of the ecard when the confirmation shows up. However, I'm not skilled enough to do the preview-while-editing, but this is a start. It's not what you want but maybe someone else can make use of this.
You will edit the file ecard.php
Look for:
if ($result) {
pageheader($lang_ecard_php['title'], "<META http-equiv=\"refresh\" content=\"3;url=displayimage.php?album=$album&pos=$pos\">");
msg_box($lang_cpg_die[INFORMATION], $lang_ecard_php['send_success'], $lang_continue, "displayimage.php?album=$album&pos=$pos");
Replace with:
if ($result) {
pageheader($lang_ecard_php['title']);
msg_box($lang_cpg_die[INFORMATION], $lang_ecard_php['send_success'], $lang_continue, "displayimage.php?album=$album&pos=$pos");
echo '<br />';
starttable('100%', "Preview of the ecard");
echo '<tr><td>';
echo template_eval($template_ecard, $params);
echo '</td></tr>';
endtable();