If I want to upload a file for download
what's determines whether that file will be
opened or downloaded?

For example:

I hosted a file with the link bellow:
www.acrisoft.bizland/dental.exe

The problem:
Instead of start download it try to execute
and return a error message.

Do I have to put something before my file ?

Obs. The server does not require HTML
code, it has an automatic builder