Vlan linux problem

Hi all i have vlan and linux configured and its ok, i can ping the
networks between the vlans but, when i tri to go to internet, i can
see some sites, but sites like webmail, msn, and other i cant open,
and i dont know what do.. i've disable the firewall and just
masquerade the network but with no sucess :( anyone has an ideia of
whats happening?

thanks