You can change anytime to and from a fullscreen more with Alt+Enter. About the speed, you can increase the CPU cycles in DosBox with CTRL+F12 (decrease with CTRL+F11), though it's easier if you just click on Edit Configuration in the DosBox shortcuts folder and change the following (it's all text there) under
[cpu] section:
core=normal
cputype=auto
cycles=auto
cycleup=500
cycledown=100
to
core=dynamic
cputype=auto
cycles=27000
cycleup=500
cycledown=100
That should start DosBox always with that amount of cycles and is enough for most games.
Edit: damn, Paco was faster
