hack – meta description with first 5 word of post

i have a simple question for us, it’s possibile insert a code string to automatic grab the first 5 word or character of posti n this section

<meta name=\”description\” content=\” \” />

<meta name=”description” content=” ” />

of theme code header.php?

have suggestion?

i use wp 2.08

thanks for support and sorry for my english 🙂