Is there any coding I can put in the url...

[tivaelydoc2]

...to make a certain word or sentance be highlighted?

For example:
http://digg.com/search?search=bill+gates&submit=Submit

[Installer]

Well, having tried them just now, it seems that both of these works:

<your example>

and

http://digg.com/search?search=bill+gates

For an exact phrase (i.e. not "Gates is a billionaire"):

http://digg.com/search?search="bill%20gates"