I am not much of a developer but have a look at the development portal I pointed out earlier.
In addition there are quite a few sample applications provided from Microsoft to give you an idea:
Ethical Walls for Microsoft Office Communications Server 2007 - Microsoft Office Communications Server 2007 API Sample http://www.microsoft.com/DOWNLOADS/details.aspx?FamilyID=070dbcab-472a-4ec1-aeac-9273eccd70c9&displaylang=en
Incoming Call Screen Pop - Microsoft Unified Communications Client API 1.0 Sample http://www.microsoft.com/DOWNLOADS/details.aspx?familyid=84AC7DD7-99D3-48F7-99D7-A281BD616407&displaylang=en
Custom Alerting - Microsoft Office Communications Server 2007 API Sample http://www.microsoft.com/DOWNLOADS/details.aspx?familyid=9EFC784B-E443-4441-926C-5FD405D41BD9&displaylang=en