There's a really handy feature in Windows Live Messenger as illustrated below that prevents instant message notifications from interrupting you while presenting. This feature should be useful any time you want to share the contents of your screen with an audience - be it your boss or whomever.
Windows Live Messenger is the latest version of Microsoft's consumer Instant Messenger application - it's available as a free download from here.
Office Communicator is Microsoft's Enterprise Instant Messenger application - it syndicates to the popular IM consumer services whilst providing the control you need to allow these services within your organisation - specifically it provides the means for confidentiality between each client and the Live Communications Server (LCS) which provides the heart of the system. Critically this system can be used to enable you to comply with corporate governance requirements which often require the auditing of Instant Messaging content.
Or you could use Messenger Plus (http://www.msgpluslive.net/) which not only adds a Boss Key shortcut (e.g. ctrl-B) to block all messenger alerts but also changes the messenger icon from the windows status bar and has a lot of other cool features as well...