HI, normally with the use of the windows key + arrow left/right, you can move a window from 1 screen to another.
To make sure that it's maximized, you could ALT+TAB.
Another way can be to make sure the windows has focus and with the ALT+SPACE, you open the system menu. With the key X you maximize the window and then again with ALT+SPACE & key M, you activate the move option. Just pressing the left/right arrow until the window appears.
Another, may more simple way, is to disable the second screen in your screen settings....
Well, all the difficult-to-understand stuff aside, For people who are.. reletively new to windows 7, and has this problem, I will simplify it for you.
1. go to Control Panel.
2. go to Appearence and Personalization.
3. go to Display
4. go to Screen Resolution.
5. On multiple displays section, scroll down, and select show only desktop one. Like this:
See the Multiple Displys Section? Select the same option as I have selected.
P.S. Click on the picture to enlarge it. I hope it helped!