Signed applets can access the local file system, but unsigned ones cannot. And to make matters worse, IE requires a signed .cab file while Netscape needs a signed .jar file. And to further complicate matters, the two require certificates in different formats for signing, and the process for signing each one is quite different. To sign a .cab file, the easiest thing to do is download Microsoft's Java SDK and sign it with that, the process is in the help documentation. The process for signing a jar file can be found in one of Sun's Java tutorials.