Newbie question about attachment

[ketulp_baroda at yahoo.com]

Hi everyone,
My application goes like this:
User can submit any attachment and can view all the attachments
submitted by other users. Attachment contents can be anything.
Now I want that if the user selects to view a particular attachment
then if the browser is able to show the attachment then it should
display the attachment otherwise ask the user to save the attachment
on the local drive.
How should I go about this??