Opening A "be Patient" Window While An Upload Completes

I have a Perl script that's called as a CGI to handle the form
submission from a browser, thru which a user from the web can up load
an image file. I would like, when the user clicks the "Send Image"
button, to pop up a small window containing an animated (working -
please be patient) .gif while the image is uploaded from thier computer
to the server, once the transfer is complete, I would like to close the
pop up window and then load the new page in the original window.

That being the said, the Perl script won't be called at all until the
upload is finished, at which point its too late to do something like
what I am describing here.

Is there a way to open this popup window as possably a child of the
current window (inwhich the user clicked the button) so that the "Be
patient window" displays the gif, then once the upload is complete and
the Perl script is finaly called, which would then update the original
window causing the popup to close automaticly?