How can I generate powerpoint files on the fly using asp,asp.net? The
generated file will contain bars and graphs generated from data from
the database.

Why did you choose Power Point format?
Those who do not have Windows + Microsoft Office installed
will not be able to view the bars and graphs that you generate.
Many output the statistics as images or PDF files.

Regards,
parubok

Direct import to powerpoint allows the end users to get the analysis
that can immediately presented (Powerpoint being the most common
presentation format).

Why not merely imbed an Excel graph into a ppt presentation? The
information that Excel has updates, and should reflect in the PPT.
Alternative to that is merely saving the Excel graph as html and the
presentation is able to be available to anyone with a browser, which
is more ubiquitous than PPT.