how does one make a email address hidden on exchange 5.5

Do you mean an outgoing e-mail address, i.e. a 'reply to' address? I doubt that you can, although if you want to send e-mails anonymously, there are plenty of dodgy little apps on the Web that will let you do it.

Ah, anonymity on the 'net. If only...
Everywhere you go you leave footprints that tell the person who you are. The chap what runs this site, for example, can tell not only where site I've come but what I do when I'm here.
Whenever you send an e-mail you're given away by the header which is invisible unless you look for it. This contains not only your e-mail address but your 'machine name'. This is what you call yourself under Network Neighborhood (right click on Network Neighborhood, then on properties, and then on identification to see this). It also contains details of your ISP and, often, your IP address.
So even if you concealed your e-mail address using Outlook -- which is possible -- the header would finger you. As the previous correspondent pointed out, you can get anyonymous e-mailers but these are very dodgy and I suspect will only work with certain types of SMTP mail servers.
If for whatever reason you want nobody to know who you are, and there are legitimate reasons for this, then use a web mailer such as Hotmail or www.another.com.