Winsock proxy with access control

[Marcelo Magno T. Sales]

Hi, people

Is there a linux/unix solution to implement Internet access control based on 
user accounts from an LDAP directory?
I know squid will do that for web access, but I'm interested in a solution 
that allows me to control internet access by protocol and by user, not just 
for HTTP. For example, I must be able to set it up so that members of group A 
can access MSN, HTTP and POP3, while users C and D can access SMTP, POP3 and 
FTP and members of group X can access HTTP and some internal applications 
which use ports 5021, 7045 and 8015.
In other words, something like what MS ISA Server does for Windows clients.
Is there a way to implement this for linux clients?

Thanks,

Marcelo