Caching and htaccess

Dear CF friends,
i run a wallpaper script on my website which is very very memory consuming and on analysis,reports of caching it are important


anyone here who can guide me on how to cache the script

i used the following code but it doesnt seem to make a difference

http://www.askapache.com/htaccess/speed-up-sites-with-htaccess-caching.html
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can any one here help me out on this?