Cause line to wrap to new line after 100 characters

Your line isn’t breaking naturally because you don;t have any spaces in it. You can use word-wrap to force the breaks, then add a max-width to say how wide it can be.

CSS

li{
    max-width:200px;
    word-wrap:break-word;
}

HTML

<ul>
    <li>Hello</li>
    <li>How are you</li>
    <li>SearchImagesMapsPla yYouTubeNewsGmailDriveMoreCalendarTranslat eMobileBooksOffersWalletShoppingBloggerFin ancePhotosVideosEven more »Account OptionsSign inSearch...</li>
    <li>SearchImagesMapsPla yYouTubeNewsGmailDriveMoreCalendarTranslateMobileBooksOffersWalletShoppingBloggerFinancePhotosVideosEvenmore»AccountOptionsSigninSearch...</li>
</ul>

http://jsfiddle.net/daCrosby/ZC3zK/1/

You’d need JavaScript to count exactly 100 characters and break the line there. Check here and here for JavaScript examples.