mount -t smbfs -o username=Whatever,password= //HOST/SHARE /mnt/point
mount -t smbfs -o username=guest,password= //HOST/SHARE /mnt/point
try these; with the null password as shown. If they're just like normal windows shares, also try replacing 'Whatever' with 'guest'. Although I'm not sure if this is strictly speaking the proper way to do it, it works when I connect to my buddy's xp pro machine.