you don't need many rules provided that you know what you want to block and what protocol it will come in on.
heres a sample site and content rule:
if you want to block all images in http://www.yahoo.com create a site and content rule withe these properties
set the rule to deny, set the rule config to custom, set the destination set path as yahoo.com/, set the schedule to always, set client type to any request, set content group to those image file extensions you dont want like .jpeg . if you want to block sounds set the content group to .mpe .wmv .wma there will be a long liste.
next you assing the site and content rule. with ISA management console open, click on site and content rules, on view menu click advanced. in the details pane right click the rule then click on properties. on the destination tab select what destinations you want. all, all external [outbound] all internal [inbound] or selected sets or all but selected set. click ok
volia! this applies to secure nat and firewall clients