fc4 samba problems

[sandman652001]

I setup samba and opened ports 137,138,139,445 on the firewall and I can reach my Linux box from windows xp but when I try to browse the samba shares from konqueror on my Linux box all I get is a "unable to find any workgroups etc. check your firewall", or on some occasions I see the windows machines on the network but when I try to access them I get a "could not connect to host for smb://hostname"
If I disable the firewall completely everything works fine

does anybody have any idea of what is happening?

Thanks for your help