I hope this answers your question:
<form action="file:///x|/" target="_blank"><input type="submit" value="Software">
The only way I got it to work is using the exact code above replacing the "x" with your drive letter, don't forget to have the pipe (|) symbol directly after the drive letter.
If you are using it to browse another server/ computer on your network simply map a drive to the machine's drive letter from your local computer.
~Johnny (Straws) Y2k06