Dear !
Its very strange that I come to know your problem so late but still I am providing the solution so that my otherfriends who visited this site can take the benefit of my advise.
So download windows resource kit from the following link.
4shared.com - online file sharing and storage - download Windows Resource Kit.zip
Then enter the following commands. (Attention: they are case sensitive.)
net user guest /active:yes
ntrights +r SeNetworkLogonRight -u Guest
ntrights -r SeDenyNetworkLogonRight -u Guest
The first command enables network access for Guest, the two subsequent ones change two different policies to allow network access for Guest.