Is it possible to configure Hudson to send build notifications to Microsoft Communicator (or Microsoft Lync) using its instant message plugin? If possible, please tell me how to do that? Thank you.
It is likely to be possible. Have a look at the existing hudson plugins, which do similar things.
If you can work out how to get Hudson to run a script once the build is complete, there's a (paid) powershell cmdlet which lets you send alerts to Microsoft Lync users.
Otherwise, you will need to find the SDK/API for Microsoft Lynq (e.g. the 2010 SDK), and write it yourself. Consider building on the existing Instant Messaging Plugin.