Excel – Network file access errors

I am running Windows XP Pro on a network with a Windows 2000 Server. I have Office 2000 w/ SP3. My Excel files are stored on a share on the Windows 2000 server. The problem is when I attempt to access various Excel files I get one of the following errors: “*.xls is locked for editing by “user”(the user is not accessing the files), or “*.xls cannot be accessed. The file may be read-only, …”. Any help would be greatly appreciated.