Berdych/Stepanek on Saturday - no matter what.
I have heard rumors saying that Rosol will play on Friday against Del Potro to save Stepanek´s energy for Saturday or Sunday.
Berdych/Stepanek on Saturday is about as certain as death and taxes.
I am also expecting Rosol to play tomorrow. The Czechs have nothing much to gain by playing Stepanek in best-of-5 singles on clay at this stage of his career. Despite the head-to-heads, I wouldn't expect him to beat either Monaco or Del Potro.
Rosol, on the other hand, has proved what he can do on a big stage (Wimbledon this year, and French Open last year), and would have little to lose in either singles this weekend. Del Potro may be visibly handicapped, which would be an opportunity. Failing that, his big game could give Monaco fits in a possible live 5th rubber. Monaco certainly the more likely to suffer nerves in that event.
A chance that Rosol could be the hero of the weekend imo.
As for the outcome of the weekend, it all rests on Del Potro. If he is fit enough to play to a good level, he should win both singles matches. Monaco should be favoured to win his match against the Czech #2 - ergo, Argentina small favourite. Also a chance that Monaco might catch Berdych sleeping on Friday - could see a 2-0 lead for Argentina after tomorrow.