1. click Start->Run, type "cmd", hit
2. a command prompt window will appear in its default size.
3. click the icon in the top-left corner of its title bar to bring down the system menu
4. click 'Properties' to bring up a dialog box.
5. (optional): in the Font tab choose your preferred font and size.
6. (important): in the Layout tab set the Windows Size to Width:100, Height:40
7. click 'ok' to dismiss the dialog.
8. close the command prompt window
Now when you run any command prompt again, it will come up in this new size. Double-click your .bat file, and the command prompt window that opens should have the new dimensions.
I am quite certain I have set my window size to Width:100 and Height:40 (other similar values have worked as well). You may be right that cgminer will crash in its default size of 80:25 ... I've never tried that as 80:25 is too small for what I like to see. Let us know how you make out.