DNN includes a Users Online module. Get it at
http://dnnusersonline.codeplex.com/. There is also a setting that must be enabled in Host Settings.
Ventrian has a "Where are they?" module: www.ventrian.com/modules/where-are-they
For birthdays, I answered a similar question here:
http://www.dnncreative.com/Forum/ta...ault.aspx. These days I would maybe do this with SGSV (tressleworks.ca) because of it's feature set, especially the templated display part.
Will you be adding a birthday field to the user profile?
Oh, the new User Profile features in DNN 7 may make this easier to do, but I havern't thought too much about it.