Hi,
maybe you should give a try locally... i mean, connect to your Ubuntu machine a try a:
smbclient -L 127.0.0.1 # that should list the available shares on the Ubuntu machine
smbmount //127.0.0.1/windows /mnt -o username="my samba user"
so if smbclient answers nothing, then you've got a problem in smb.conf
if smbmount hangs, either you've got a problem with users (don't forget that you need to create samba users with the smbuseradd command), or the path to the shared directory is not good (it must be the same as appear in smbclient output).
if everything works, then maybe you've got a firewall running, or the networking service in windaube isn't started or smtg esle
good luck