Windows – Problem modifying read-only files on Samba NAS

I have files on a Samba server in the local company network and accessing them from a Windows Vista machine. Usually, if I want to delete a directory containing read-only files, Windows simply deletes the whole folder anyway. However, when I do this with a dir on the server, Windows just tells me that I need permissions (screenshot of an identical error message, just different file). The workaround is to remove the read-only flag from the directory and all contained files and then deleting. However, I have a TortoiseSVN versioned dir on the server, and the .svn dirs contain read-only files. I need to remove the read-only flags from the dir before every commit, or else it fails. This is quite distressing and shouldn't be so. Does someone know how to attack this problem? (If someone knows how to tell TortoiseSVN to not make its files read-only, that would probably be ok as well) … Thanks!

EDIT:

The file in question is a shared file, i.e. I have no specific user account on the Samba server. Owner is nobody, and everyone has all rights to the file. If (in Windows) I set the file as "readonly", then (in Linux, Debian Lenny, where Samba is installed) everyone suddenly has absolutely no rights on the file anymore. If I remove the readonly flag, everyone has all rights again.

Here is the Samba config file smb.conf:

# Samba config file created using SWAT
# from 192.168.1.200 (192.168.1.200)
# Date: 2006/08/25 17:14:50

# Global parameters
[global]
        workgroup = FIRMA
        server string = %h server (Samba %v)
        security = SHARE
        obey pam restrictions = Yes
        passdb backend = ****
        passwd program = ****
        passwd chat = ****
        syslog = 0
        log file = /var/log/samba/log.%m
        max log size = 1000
        dns proxy = No
        panic action = /usr/share/samba/panic-action %d
        include = /etc/samba/dhcp.conf

[homes]
        comment = Home Directories
        create mask = 0700
        directory mask = 0700
        browseable = No

[shared]
        path = /baldur
        read only = No
        create mask = 0777
        directory mask = 0777
        guest only = Yes
        guest ok = Yes
        map archive = yes
        map system = yes
        map hidden = yes

EDIT 2:

baldur:/baldur/Mitarbeiter/Felix/Praktikum/projektrenate# ls -ld .svn
drwxrwxrwx 6 nobody nogroup 4096 15. Dez 19:34 .svn

baldur:/baldur/Mitarbeiter/Felix/Praktikum/projektrenate/.svn# ls -al
insgesamt 32
drwxrwxrwx 6 nobody nogroup 4096 15. Dez 19:34 .
drwxrwxrwx 5 nobody nogroup 4096 15. Dez 13:37 ..
-rwxrw-rw- 1 nobody nogroup   77 15. Dez 18:19 all-wcprops
-r-xr--r-- 1 nobody nogroup  236 15. Dez 18:19 entries
drwxrwxrwx 2 nobody nogroup 4096 15. Dez 12:56 prop-base
drwxrwxrwx 2 nobody nogroup 4096 15. Dez 12:56 props
drwxrwxrwx 2 nobody nogroup 4096 15. Dez 18:19 text-base
drwxrwxrwx 5 nobody nogroup 4096 15. Dez 18:19 tmp
baldur:/baldur/Mitarbeiter/Felix/Praktikum/projektrenate/.svn# less entries
baldur:/baldur/Mitarbeiter/Felix/Praktikum/projektrenate/.svn# ls -al
insgesamt 32
drwxrwxrwx 6 nobody nogroup 4096 15. Dez 19:34 .
drwxrwxrwx 5 nobody nogroup 4096 15. Dez 13:37 ..
-rwxrw-rw- 1 nobody nogroup   77 15. Dez 18:19 all-wcprops
-rwxrw-rw- 1 nobody nogroup  236 15. Dez 18:19 entries
drwxrwxrwx 2 nobody nogroup 4096 15. Dez 12:56 prop-base
drwxrwxrwx 2 nobody nogroup 4096 15. Dez 12:56 props
drwxrwxrwx 2 nobody nogroup 4096 15. Dez 18:19 text-base
drwxrwxrwx 5 nobody nogroup 4096 15. Dez 18:19 tmp
baldur:/baldur/Mitarbeiter/Felix/Praktikum/projektrenate/.svn#