hey i've been looking for the chords as well to play on either - here are a couple sites I found that were helpful:
<a href="http://www.e-chords.com/guitartab/idmusica/93680.htm" target="_blank">http://www.e-chords.com/guitartab/idmusica/93680.htm</a>
(at least the C# chords at the beginning of the chorus are not right)
And this was a little helpful as well, but not as much.
<a href="http://www.8notes.com/scores/9668.asp" target="_blank">http://www.8notes.com/scores/9668.asp</a>
The intro (which I would guess is not the part you're having any issues with, but still) is here:
<a href="http://www.ultimate-guitar.com/tabs/r/rihanna/unfaithful_intro_ver2_tab.htm" target="_blank"> http://www.ultimate-guitar.com/tabs/r/r … ithful_int ro_ver2_tab.htm</a>
I hope any of this is helpful, and if you figure it out, let me know <img src="images/smiley_icons/icon_smile.gif" border=0 alt="Smile">