Copied from a tutorial I found on another website while looking for the same thing:
Expiration
If you want to have your page "expire," here's how to set it:
<META HTTP-EQUIV="expires" CONTENT="thu, 31 DEC 2002 00:04:00 EST">
What this means in the real world is that your visitors' browsers will use the cached version of your page, if available, until the specified date and time are reached, at which time the page will reload from the server the next time it's visited. To force your visitors' browsers to reload your page from the server (i.e. always use the most recent content) on every visit, use the following:
<META HTTP-EQUIV="expires" CONTENT="0">
META Cache-Control
This tag keeps your page from being automatically cached by servers or browsers. AOL, for example, usually stores cached pages on its servers, which means that AOL users may view cached (i.e. old) copies of pages without being able to see the updated versions. Although caching pages speeds loading times, if your page is updated frequently, I suggest you use the no-cache tag to make sure your visitors always get the most recent version of your page:
<META HTTP-EQUIV="Cache-Control" CONTENT ="no-cache">
The following tag works specifically on Netscape browsers:
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
What I think berg meant was indeed that he wants to prevent his visitors to use cache versions of his site, so that they always get the most recently updated versions of the pages.
There's also some javascript coding which according to another website is the preferred way, but I don't really see how these ways differ to the visitor, so perhaps that's just a matter of taste.
Then again, I'm not a real expert, I just play one on IRC
