I like your work ethic, continual improvement, but I have to
side with Abigail-II here. As Aby (can I call you Aby?) points
out. Using this script will not keep anyone from putting a file
with duplicate names on you site. I would just give you a way
of fixing the problem.

If your on a unix box try setting the sticky bit on your upload
directory. That should keep anyone but the owner of a file from
over-writing a file that already exists.

Of course, if sounds like you are staging the data before allowing
it to be posted... which is very wise.