Is it possible to substitute a custom appointment dialog? If so is there a sample somewhere? Is it necessary to inherit AppointmentDialog--what would be the advantages of inheritance?
Take a look at the following article:
http://devcenter.infragistics.com/Support/KnowledgeBaseArticle.aspx?ArticleID=3882
Also, the following article will tell you various ways to upgrade a WinForms application that uses Infragistics controls (the sample in the previous article uses an older version) :
http://help.infragistics.com/Help/NetAdvantage/NET/2008.1/CLR2.0/html/Win_Upgrading_Your_Windows_Forms_Projects.html