Mac users can’t modify Windows 2003 FTP files

I have recently created a FTP server with Windows 2003 Enterprise Edition. Users can access and modify files fine from a PC, but Mac users can’t. They can access the FTP site and see everything in it, but when they try to upload a file, it says they can’t modify it. I have the correct permissions set but it doesn’t help.

Also, I isolated the users to be able to only see their folders/files, but when using Firefox or IE7, they can see a link that allows them to go higher up the directory and see everyone elses folders and files. How do I correct this?

Any information on both subjects will be helpful