There are two forms of file system permissions, share and NTFS. Windows 2000/XP sets the share permissions to Everyone - Full Control. Windows XP SP1 and Windows 2003 changed that to Everyone - Read Only.

That is ok, as you can lock down access rights with NTFS Permissions, however it is a best practice to remove the Everyone group, and add the Authenticated Users or Domain Users group to the Share permissions and give them Full Control.

Then use NTFS Permissions to control access. Remember the most restrictive of the combined permissions is what gets applied and Deny overrides everything!