It depends on what you're trying to write but personally I'd go for installing Visual C++ 2010 Express and see if that meets your needs. It's targetted at C++ but there's no reason why you couldn't use it to write straight C if that's what you need. Also depends on where you want to deploy as it's targetted at Windows. Otherwise I'd look at using GCC as my compiler and somethig like notepad2 as my editor if I wanted to work outside an IDE.
EDIT: Possibly this didn't actually answer your question. DOSBox is a DOS emulator used more for running legacy software than writing new software I would have thought.. so if you're writing new software I'm not sure that using DOSBox is necessary or the way to go?