I run my webserver and file server from a virtual machine with the files shared using Samba (yes, now that I’m running on OSX I should really share the files with NFS but that’s for another day). When trying to copy files from the Mac to the Samba share I was getting the error message "The operation can’t be completed because you don’t have permission to access some of the items".
The solution, as posted at splatdot.com is to set "unix extensions" to "no" in the global samba settings on the fileserver host machine. Read the full post "Fixing Snow Leopard 10.6.3 Samba Write Access" for more details.
It will pay to manually unmount the shares on your OSX machine first before restarting Samba on the fileserver otherwise you may have issues with Finder/bash locking up (this happened to me the first time I shut down a Windows box I had a share mounted from).
Anway, that post is what I found after searching for the issue so go have a read and hopefully it wil fix your issue too.