yes.. u can..
to block.. *.mp3 files..
u have to make sure that ur squid is compiled with delay pools enabled...if yes.. then put the following line.. in squid.conf
acl magic_words2 url_regex -i ftp .exe .mp3
delay_class 2 2
delay_access 2 allow magic_words2
to deny accessing a site..
acl blocked dstdom_regex .yahoo.com abc.com
http_access deny blocked