Ah, ok, now I kinda get what you want. But what about a simple something like this?

print header;
print <<EOF
<script language="JavaScript">
alert('Hello World');  
history.go(-1);
</script>
EOF
;
[download]

This way, you will get your popup and the user will go straight back to the previous page which probably is still cached (if JavaScript is turned on ... of course). For simple forms, this should be ok.

You got it. And yes, it does seem that it isn't possible without intervening javascript before going to the cgi code. For doing simple forms, that's not so bad. But when you don't know whether data in a form isn't right until you've gone to the server side (which may require doing db searches, etc.), you're basically forced to redraw the page... and that may also be an equally expensive operation.