I’m running Linux Mandrake 8.0 and WinXP boxes on my home network. Everything works fine except that for some reason when I try to edit a document that was created on the Linux box from the WinXP box I get permission denied, and I get the same when I try to create a new document on the Linux box from WinXP, and the same when I try to perform these task on the Linux box for documents on the WinXP box. The documents that I’m editing and creating are text documents.

I do have the permissions setup for me to read, write and execute for both boxes, I get the same message if I’m logged on as Admin or root. If I’m at the keyboard of either box and create or edit a document I don’t get this message, so it seem as though I have permissions to perform these task, but not over a network.

In linux, if you try to chmod 777 file, can you then modify it in windows? If yes, then it's a permissions issue.

Check your smbusers file.
With host:linux client:win, what is the windows user? Administrator? what linux uid is the Administrator windows user mapped to in smbusers?

Or, another thing to try (or might want to do anyway) is updating to latest Samba server..