I personally use XFIRE myself, though I don't use the XFIRE MSN plugin so I can't speak for that, but there is another application that has promise I have been following, still in early stages and not as stable
(on a 64bit system, at least) called
PlayXpert.
I use it on a limited basis seeing as how 64bit support is still flunky, but it allows you
(like xfire) to bring up an overlay in game, but where this is better than Xfire (in idea) is that it allows you to connect to multiple messengers at once, such as MSN, AOL, ICQ, GTalk, Yahoo, and even your XFire account. Give it a shot, you may like it.