If you stop any computer from caching anything, you stop the computer.

In order to perform any operation, any computer must copy the program and data to RAM. Since RAM is seldom sufficient to hold all the information needed for operation, the program and data must be written to cache, in the form of Temporary files, from which it can be swapped into and out of RAM to perform necessary "computing" functions.

If you mean "how do I stop Vista from displaying a page from memory instead of downloading a fresh page?" that setting is made in your browser.

In IE, click Tools on the top toolbar, select Internet Options, On the General Tab, at Browsing History, where it says "Delete Temporary Files etc." click the button labelled "Settings" and select one of the options to tell IE when to check for new pages.

I can't advise how to change the settings for other browsers, since I'm not smart enough to manage more than one, so I don't have any others.

If you mean "How do I keep Vista from remembering where I've visited" about the best you can do is a Disk Cleanup that can delete all your Temporary files. You can delete most temp files in IE, but a program that is open cannot be deleted, so the best procedure is to close all programs except Windows Explorer, Right-click on a drive and select properties. On the general tab, click "Disk Cleanup."

If you mean "I've been naughty and need to keep the government agents from finding evidence of it," you need to reformat all your drives, then smash them into little pieces, burn the pieces in a fire hot enough to melt most of them, and then dissolve what's left in strong chemicals and get new drives. Like all operating systems, Vista keeps some logs that are necessary for "diagnostics and repair" that are very difficult even to find let alone to remove completely. There are enough of them that it's impossible to tell which one(s) might contain the information you find embarrassing. The intent is not to convict you of anything, but any of them could possible contain something incriminating.

John