Just go to Google Fonts - http://www.google.com/fonts/ , add the font you like to your collection, and press the download button. And then just use the @fontface to connect this font to your web page. Btw, if you open the link you are using, you'll see an example of using @fontface
http://fonts.googleapis.com/css?family=Open+Sans:400italic,600italic,400,600,300
For an example
@font-face {
font-family: 'Open Sans';
font-style: normal;
font-weight: 300;
src: local('Open Sans Light'), local('OpenSans-Light'), url(http://themes.googleusercontent.com/static/fonts/opensans/v6/DXI1ORHCpsQm3Vp6mXoaTaRDOzjiPcYnFooOUGCOsRk.woff) format('woff');
}
Just change the url address to the local link on the font file, you've downloaded.
You can do it even easier.
Just download the file, you've linked:
http://fonts.googleapis.com/css?family=Open+Sans:400italic,600italic,400,600,300
Name it opensans.css or so.
Then just change the links in url() to your path to font files.
And then replace your example string with:
<link href='opensans.css' rel='stylesheet' type='text/css'>