use ipchains to block ports

hi there ,

I'm not familiar with linux firewall .
I tried to block port 6891 thru 6900 to disable msn messenger file
transfer.

following is the result of my linux ipchain -L :

Chain input (policy ACCEPT):
target prot opt source destination
ports
DENY tcp ------ anywhere anywhere
any -> 6891:6900
ACCEPT all ---f-- anywhere anywhere n/
a
acctin all ------ anywhere anywhere n/
a
acctboth all ------ anywhere anywhere n/
a
inp all ------ anywhere anywhere n/
a
Chain forward (policy DENY):
target prot opt source destination
ports
DENY tcp ------ anywhere anywhere
any -> 6891:6900
ACCEPT all ---f-- anywhere anywhere n/
a
fwd all ------ anywhere anywhere n/
a
Chain output (policy ACCEPT):
target prot opt source destination
ports
DENY tcp ------ anywhere anywhere
any -> 6891:6900
ACCEPT all ---f-- anywhere anywhere n/
a
acctout all ------ anywhere anywhere n/
a
acctboth all ------ anywhere anywhere n/
a
out all ------ anywhere anywhere n/
a
Chain acctin (1 references):
Chain acctout (1 references):
Chain acctboth (2 references):
Chain inp (1 references):
Chain out (1 references):
Chain fwd (1 references):
target prot opt source destination
ports
DENY udp ------ anywhere anywhere
any -> 6891:6900
DENY tcp ------ anywhere anywhere
any -> 6891:6900
DENY tcp ------ anywhere anywhere
any -> 6891:6900
DENY tcp ------ xxx.xxx.xxx.0/24 anywhere
any -> 6891:6900
DENY tcp ------ anywhere xxx.xxx.xxx.0/24
any -> 6891:6900
MASQ all ------ xxx.xxx.xxx.0/24 anywhere n/
a
MASQ all ------ anywhere xxx.xxx.xxx.0/24 n/
a
MASQ all ------ xxx.xxx.xxx.0/24 anywhere n/
a
MASQ all ------ anywhere xxx.xxx.xxx.0/24 n/
a


can anyone help me to block port 6891 thru 6900?
I tried and tried , but it just won't work?

please show me the right rule to block these ports.

any message from you will be appreciated.

tks .