I have used the following:

Transmit Holidays Form
http://www.slipstick.com/dev/olforms/holiday.htm

I have tweaked this a little and created a public folder where my clients go
and use this form. You can use it to mail it out too. There is also a way to
replace each clients outlook.txt file that works quite nicely. You just edit
the "Outlook.txt" file and distribute it to each of your clients via SMS or
similar. I really like this method because you can place just your "Days
Off" (not necessarily the legal Holiday) into the file, the clien uses
Outlook in the normal fashion and they really don't know that a change has
taken place.

Nikki;
we have a locked down environment so the use rcannot apply the updates to
the local machine. can the Outlook 2000 Add-in: Holiday Updates be applied
to the server so that all users get them at once?