Nashville is a very solid team top to bottom. Only weakness in roster construction is (obviously) they don't have those 2 top end scoring players that can put up offense every night. Overall they play a very strong possession game - I think they are 12th or 13th best shot differential in the league at even strength, compared to Dallas at 8th.
The thing that has really let them down this year (as other have mentioned), and will hopefully give the win to Dallas tonight, is that they have got absolutely horrible goaltending performances from all of their guys.
Basically I wouldn't say that Columbus is all that more difficult opponent than Nashville is at this point. I think the most important result tonight is a Phoenix regulation loss, and a win for Dallas will be icing on top of that if it happens. Nashville has shown recentley they can hang with any team in the league though (even with the bad goaltending) so I wouldn't be shocked if the Preds take this one tonight.