Ms network browser problem

hi all, i manage a network of 120 windows xp systems and my gateway run on centos 4.6 i actually config the linux gateway my self and i config iptable rules as well.until now, all has been fine but the problem now is that amunable to browse the network using my network places from some of the windows pc.i know such issues normally has to do with blocked ports but i didn't block the port used by windows for file sharing.how to i resolve the problem?

Thanks.

I don't see how this is related to this forum, looks like windows problem to me.
The only thing I see here is that Linux is your gateway. Unless your Linux is a gateway to some other subnet where your XP systems are sitting.
Please be more specific.