nat/masquerade with 2.6.x

["Antonio Pérez" <aperlu@telefonica.net>]

Hello,
I have a local network with private directions, and a adsl conection. I 
want to do masquerade. Then I do:
   echo 1 > /proc/sys/net/ipv4/ip_forward
   iptables --table nat --append POSTROUTING --out-interface eth1 -j 
MASQUERADE
where eth1 is the interface conected to internet. This work perfectly 
with the kernels 2.4.x.
But one week ago I installed the kernel 2.6.8 and when I do :
   echo 1 > /proc/sys/net/ipv4/ip_forward
   iptables --table nat --append POSTROUTING --out-interface 
$ifc_internet -j MASQUERADE
the hosts of the internal network can do ping to internet, and this is 
normal, but they can not open any web or conection the msn , they
only can do ping. This is very stranger. I try the kernels 
2.6.7,2.6.7,2.6.8 and 2.6.9 and they do no work.

I know that the dns is working because when I do "ping www.google.es" 
from  internal host  this  work.
There are not other rules in the FORWARD chain, look:

   Chain INPUT (policy ACCEPT 2 packets, 100 bytes)
       pkts      bytes target     prot opt in     out     
source               destination

   Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
       pkts      bytes target     prot opt in     out     
source               destination

   Chain OUTPUT (policy ACCEPT 5958 packets, 2480411 bytes)
       pkts      bytes target     prot opt in     out     
source               destination

and if i do iptables -t nat -L -nvx, then:

   Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
       pkts      bytes target     prot opt in     out     
source               destination

   Chain POSTROUTING (policy ACCEPT 1 packets, 60 bytes)
       pkts      bytes target     prot opt in     out     
source               destination
          0        0 MASQUERADE  all  --  *      eth1    
0.0.0.0/0            0.0.0.0/0

   Chain OUTPUT (policy ACCEPT 1 packets, 60 bytes)
       pkts      bytes target     prot opt in     out     
source               destination

And this is all,
Can somebody help me, please?
Sorry for my bad english.