We are looking at some applications where we support both Lotus Sametime and Microsoft OCS - but provide a nice web UI. It's a frequent dilemna: Java or .net. For this application, I'm inclined to use .net - mainly because there are so many great charting components.
However, I don't want to limit our deployments to just shops where they run IIS. Here is a background article on asp.net and running without IIS.
An article on Cassini: http://www.devx.com/tips/Tip/30771
Article by Eric Pearson: http://geekswithblogs.net/ericpearson/archive/2005/11/25/61201.aspx