Ummm.......if Samba or internet sharing doesn't work without shorewall there must be another firewall in place. Can you at least ping the server now?
In any case, Mandrake is probably the last distro I would use for a server. It's really geared towards desktop use in my opinion. I mean the standard install doesn't even have sshd on it!!
Good luck though dude....you asked the question in the right place at least!!