tCalDate is a FreeWare for non commercial sites, it means its use is free.
For personnal use, I'd like you to add a link to the author (link to javaside.com) and send me the URL of the page which uses the tCalDate applet.
For a professional use, you have to get a "professional registration". This registration allows you to use tCalDate without reference to the author and I will send you back the complete source.