Paul
    My current employer also uses exchange, I use a Mozilla Thunderbird and The Lightning plugin for calender support. Lightning allows me to subscribe and send calender events.
This requires that your employer turns on IMAP support in exchange, which is a simple enough task. They only thing you can not do it use shared calenders.  This works on NetBSD 3.1 on i386. 

-- 
]Mark Saad[
mark AT bad-apples.org