I've heard some people say they don't like to use frames, but for me, I always use frames for the sidebar, or menus so that I don't have to change every page individually everytime I need to change the sidebar.
Is there anything besides frames that I could use to make it easier?
And what are the ups and downs of frames?

What is asp.net?
Also, I've heard about ssi but I'm not sure how it works.
I've tried using iframes but it doesn't seem to work, it gives me an error message that says the error is "permission denied". If I could get iframes working, would they be better than frames to use? The problem I have with frames is that my sidebar is longer than the page so it just dissapears at the end of the page.
Is there any other alternative?

Yeah use a serverside language like PHP or ASP and then have a content management system using a database