Default Group Ownership and Permissions

Question

All new files created by a standard user (User1) have group assigned as "staff" and group permissions set to "Read only."  How do I change the default group and ownership permissions for newly created files?
Said another way: I want new files created by User1 to have group = "Accounting Group" and group permisions = "Read & Write".

Answer 1

You can accomplish what you want to do by using ACLs. First go to System Preferences -> Users & Groups, and make a new group called "accountinggroup". Add the users you want to the group.
You will then need to make a folder in which to store all the files to be shared with this group. Put it in some easily accessible place like in /Users/Shared.
Then log in to an admin account and open Terminal. Paste in all of this and the press return:
sudo chmod -R +a "accountinggroup allow delete,chown,list,search,add_file,\
add_subdirectory,delete_child,file_inherit,directory_inherit" \
Then drag the folder into the Terminal window and press return again.
From then on, any file that is newly created in or copied to any location within that folder hierarchy will have read and write privileges for all users in accountinggroup.
You sir are a genius.
I have been trying to utilise a users iMac a "central file storage" for a small business client (all new Lion Machines). I was having so many issues with Lion's POSIXs permissions and also Lion's new versions feature.
Every time users saves files to the shared folder they would inherit permission from the computer that created the file. Thus is another user logged on and opened the file it would be 'Locked' and have to be duplicated or the users would have to manually edit permission using 'Get Info'
I have applied the ACL via terminal and now it works like a dream! All files have that are put into the shared folder have a group with 'custom' permissions and any one can use and modify the files, provided they have log in credentials.
The only trap i would warn people of is do not use typical group names like "Staff", "workgroup" etc. I found that using those was problematic. I opted for employees.
Thanks again Király