OK, the problem here isn't getting something fancy to scroll across the top of the forum web page - It's figuring out where you want the message to come from.
Are you posting ops on the Calendar feature of your corp forum? If not, why not?
To get something appearing at the top of your forum page you can use something like http://www.rsspump.com/
which will link to an RSS feed. SMF can generate RSS feeds for you. Enable them on Admin -> main -> Newsletter & news.
If you haven't got anything to post your corp ops on then have a look at -> http://www.eveonline.com/ingameboard.asp?a=topic&threadID=1449246
At the moment its only for posting POS Timer ops, but if there's enough demand then I can modify it to replace "POS Timer" with "Mining Op" or "CTA" without too much trouble. There will be a new version with an RSS feed available in a couple of days.