how can i send a document from my pc to my fax machine?

there's plenty of fax services on the internet - try http://www.efax.com/ - i think it's free to sign up - once you have an account you can use your efax account to fax a document to your real fax machine

I think some versions of windows have fax drivers built in - some basically you open the document and print to the fax driver - assuming you have a modem - bingo

There are many different Internet fax companies out there.

Here is a list of the Top 10 Online fax services available http://faxing-service-review.toptenreviews.com/