I have Mandrake 10.1 with Samba 3.02 and squid 2.5.
The problem is that we can not access directories other than home directories from Windows XP. A dialog box inform us that cat not access the sharing folder or sometimes ask for user/password with no results.

For testing, I created a samba user with the same login name/password as windows.

The smb.conf:
[global]
workgroup = MDKGROUP
#netbios name = md_group
server string = File Sharing Server %v
map to guest = Bad User
security = user
encrypt passwords = yes
null passwords = Yes
username map = /etc/samba/user.map
log level = 3
log file = /var/log/samba/log.%m
max log size = 50
socket options = TCP_NODELAY SO_RCVBUF=8192 SO_SNDBUF=8192
printcap name = cups
domain master = Yes
os level = 51
dns proxy = No
printer admin = @adm
printing = cups

[printers]
comment = All Printers
path = /var/spool/samba
read only = No
create mask = 0700
guest ok = Yes
printable = Yes
print command = lpr-cups -P %p -o raw %s -r # using client side printer drivers.
use client driver = Yes
browseable = No

[print$]
path = /var/lib/samba/printers
write list = root, @adm
read only = No
inherit permissions = Yes
guest ok = Yes

[pdf-generator]
comment = PDF Generator (only valid users)
path = /var/tmp
printable = Yes
print command = /usr/share/samba/scripts/print-pdf %s ~%u //%L/%u %m %I "%J" &

[homes]
browseable = no
comment = Home Directories
writable = yes

[testshare]
comment = /root/testshare
writeable = yes
public = yes
guest only = yes
path = /root/testshare

for obvious reasons you can't make a directory /root/testshare and have anybody but root access it

Ok. But why I can not create sharing directories outside root and I have root priv?

Be sure the folder/files you have shared has the proper permission (read,write,execute) for other users and groups to have access to.

The permissions for the sharing folder (testshare) are 777.
Also, why I can not sharing a folder outside my home folder as I have root priv?

Out of curiosity.....just try this in your Global settings and see if you get somewhere
security = share

When I'm setting security = share then the login name for the sharing directories is always guest and never login.
(Also, I set the samba password.)
Any ideas to check out ?

Did you specify a different account for guest logins? In smb.conf, there is a guest account settings, its default is user nobody. But you can specify a different account for guest logins.