Is there a way to disable a Linksys WRTP54G router so that users CAN NOT stream audio or video. I only want them to be able to send/receive emails and upload or download pictures within emails.
The default software for Linksys routers doesn't normally provide this level of URL filtering. You may find that iptables on DD-WRT (http://dd-wrt.com/) or even OpenWRT may work for you.
Netfilter (which we usually see as iptables) helps us filter on:
A quick Google search offered up this:
NOTE that the Layer7 filter HOWTO page's "actually doing stuff" section (http://l7-filter.sourceforge.net/HOWTO-kernel#Doing ) says "Instead of dropping packets you don't like, [use] Linux QoS" to limit their available bandwidth, which it then briefly describes.
(note that I have no connection to L7-filter or clearfoundation.com, nor 1st hand or 2nd hand knowledge of their product - just what I read on the 'net...)