I know Chessmaster does this (see Ubisoft's list of controls for Chessmaster X), since I've used Chessmaster X. In certain (i.e. non-competitive) game modes, Ctrl-F will force the computer to move during its turn. It isn't a free program, but it has a lot of good resources for a beginner which IMO make it worth it.
Edit: It looks as if I have misread the question; I believe you actually meant the player can force the computer to make a certain move when it is the computer's turn. As far as I know, you cannot do this without setting up the board to a certain position, then playing from that position. E.g. you are White:
1. e4 e5 2. Nf3 ... and you want to make the computer play
2... f6 to practice your advantage against this opening. In this case, you would set up the board manually (which Chessmaster as well as most other chess programs allow you to do) as
FEN rnbqkbnr/pppp2pp/5p2/4p3/4P3/5N2/PPPP1PPP/RNBQKB1R w KQkq - 1 2, and play as White from there In most programs, including Chessmaster, you can manually move around/add/remove pieces to attain the desired position.