Hope I'm not too late with my reply, I just saw your question. Do you have any target species in mind? Have you birded the eastern US before, or is this your first time?
I'm much more familiar with the birding areas around Fayetteville (45 minutes to the north of Ft. Smith), but there are a few suggestions I can make. The first place that comes to mind is the Janet Huckabee Nature Center
http://www.rivervalleynaturecenter.com/ which has a nice feeder set up, a boardwalk through some wetlands, and a lot of quiet roads through woodland and shrubland.
Another option is Springhill Park in Barling (a suburb of Ft. Smith), it's right along the Arkansas River, in October there should be American White Pelican and possibly several duck species. There is also some good woodland habitat. I can't find a proper website but the location of this park can be found at
http://www.reserveamerica.com/campgroundDetails.do?subTabInex=0&&contractCode=nrso&parkCode=sprh
NW Arkansas Audubon's page on birding hotspots is mostly geared towards the Fayetteville area, but some may be worth considering:
http://www.nwarkaudubon.org/id17.html
Frog Bayou isn't too far from Ft. Smith and is one of the better wetland areas in this part of the state. Devil's Den also isn't too far (maybe 30 minutes?), it's a very scenic park with some nice trails, good for forest birds.
Hope this helps, feel free to send me a pm if you have any questions or any target species. Good luck, and welcome!