can someone help me with DOS?

i got this old computer game that runs on DOS. and i can play it but its wicked fast on my computer, so i downloaded this thing called DOSbox. but when i go into DOSbox, i cannnot open the .com file. i dont understand. i can see it in the dir but when i type the name or run or anything i am stuck at the C:\> prompt…..

help? anyone?

nevermind, i fingered it out, but another question arises…..when i maximize my DOS window, its not centered, so i cant see the whole screen….how can i center it?