Is DosBox 16-bit? If it is I'm afraid 7 won't work. If it's 32 bit the installer might complain but you can just manually extract the files and it will almost certainly work. 7 is way WAY more compatible with pretty much everything than Vista is.
I see your age is 21, are you in college? Ask about your school's MSDNAA program. You might have to take a 100 level programming course or something but it's worth it for all the free software. I have every current 64 bit OS, xp pro, visual studio, and some various other things that I got for free through my college.