I read in a post (I think to Slashdot) that Ruby was found to have stability problems when there was a certain number of users. I will post what I've just Googled, but I can't remember the original article.
http://almaer.com/blog/ruby-is-not-r...finitive-proof
http://developers.slashdot.org/artic.../05/02/1516208
These two posts specifically refer to Ruby on Rails, though. This may make a difference. But you could also look into the history of the different scripting languages. This may help you decide.
Ruby
http://www.rubytips.org/2008/01/10/a...-ruby-history/
Python
http://en.wikipedia.org/wiki/History_of_Python
Perl
http://en.wikipedia.org/wiki/Perl
PHP
http://www.php.net/manual/en/history.php.php
Another choice is to create a Flash based website. Or use OpenLaszlo to create Flash and DHTML. It has a very simple syntax with a heavy focus on Javascript, which is standard in most browsers anyway.
Or, you could wait for HTML 5 to become a standard and hope that everyone upgrades to an HTML 5 compliant browser. That would be great. No need to worry about what language to use.
The final question, which should have been the first question, is why do you want to rely on a scripting language to do visual and audio? Most scripting languages "flash" up the site but are mostly important in forms. Posted information is translated by these languages.
I think that it goes without saying that Apache will be your web-server of choice, but this is debatable.
It would be nice to know what your target audience is and how many people you are catering to.