My Trial version of Autodesk Revit Structure 2009 expires after 30 days. Now I cannot save my file.
 
Can somebody tell me how can I use it again saving my file.  I still want to try this version.
 

If you are a student, you can use student's unlimited version (for non-commercional using of course).

thanks pePar..
 
Is it downloadable on the web?

Yes, http://students.autodesk.com .