You should now have IMAP mail under netscape. Please note again, when you send a mail it will not be copied up to the exchange server, but to your local mail, and you'll have to drag and drop to copy the mail onto the exchange server. Please try to upgrade. At time of writing, Netscape 4.61 handles IMAP very well. In college, over a fast network, this works very well, and is the recommended way to do it.
All commands are server-drive, and the client merely displays the data.
Mail is downloaded to your local PC, and once it's downloaded it is usually deleted from the server. If you go to a different machine like your home PC, the messages on your office PC are inaccessible. Since IMAP and Exchange are very similar, the exchange server can fake it better, and things work better all around. Also - when at home, you have access to mails you read at the office, and vice versa. This is a big win.