You can add XML Doc comments above your class declaration by simply typing ''' (three single quotes in a row) on the line above your class. A small template will appear and you can fill in your summary information. Hope this helps!
If you are using VB.NET and not VB2005, then you need to use an Addon.
http://msdn.microsoft.com/vbasic/default.aspx?pull=/library/en-us/dv_vstechart/html/VBGeneratingDocs.asp
Regards,
Vikram