Didn't know what the "Xfire" was until I did a quick search for it. It's like a Friends List / Instant Messenger type program right?
RailWorks uses the Steam-client, and the Steam-client has it's own built in community overlay when running games. So, it could be conflicting in that regards.
First you might try un-checking the "Enable Steam Community in game" option for the RailWorks properties from within the Steam-client.
If that doesn't work, then I might suggest a work-around of sorts that may still allow you to run your Xfire program by playing RailWorks in windowed mode (from the launcher, Settings, un-check "Fullscreen" option, be sure to select a resolution suitable for a window, "Test" settings, if good, then save and play).
For an official list of RailWorks DLC from the Steam-Store, check out this link:
http://store.steampowered.com/dlc/24010/Take a look over that list and see what grabs your attention.
If you act quick (a little over 5 hours remaining as I write this message), there's still a few hours of the Summer Sale in which you can get 50% off on RailWorks and DLC.
Rich's Garber's routes have a North American style to them which you might like.
He's made routes like; Rascal & Cottonwood, Colton & Northern, Fort Kent to Eagle Lake and Ohio Steel - Dover Division.
You can buy from the Steam-store, or you can check out his site over at:
http://www.allaboardrails.com/If you look around, you can also find some free goodies for RailWorks too.
I might suggest to look within RWA's own File Library here:
http://railworksamerica.com/FileLibrary/ Welcome aboard to the wonderful world of RailWorks.
See you on the trains.

---Don.