Is it a copy/past. If it is, be careful with to the two time /dev/sdb2 entry, but i'm sure it's just a typo in the message (otherwise you'll have an other error).
/dev/sdb2 /mnt/Widows ntfs-3g ro,defaults,locale=en_US.utf8 0 0..
/dev/sdb2 /mnt/WinUser ntfs-3g rw,defaults,locale=en_US.utf8 0 0
gnome or kde ? In gnome, only device mounted on /media can be show as an icone, you should change the mount directory if you want to use them like that. If you use kde, i can't really help you.
Unable to mount the selected volume.
>Show more details
mount: according to mtab, /dev/sdb1(/dev/sdb2) is already mounted on /mnt/windows (/mnt/winuser)
But your partitions are mounted for sure.
You should always be able to browse them with nautilus konqueror or even the command line, by going to /mnt/Windows or /mnt/WinUser