timppu: That depends on the graphics drivers, I guess? I prefer playing older 4:3 games also in 4:3 aspect ratio (with black bars on both sides), and I think they all do that just fine on all my PCs, both DOSBox and Windows games. Even when I am using my TV to play them. Occasionally I've had problems where the TV likes to stretch 4:3 games (and maybe also TV programs) to 16:9, but lately that hasn't been an issue.
Dune 2000 was tricky though as it apparently uses some odder resolution which isn't exactly 4:3 nor 16:9 I think, so normally it would be displayed in a window with black bars on both sides and up/down. I was able to make it fill the screen properly though with some tinkering, using the PowerStrip utility.
I still prefer playing some games sometimes in a windowed mode:
- If I want an easy access to some PDF manual or text file (the game manual, or FAQ/walkthrough) while I am playing it. Somehow easier to switch back and forth when the game is in windowed mode, more instantaneous.
- If I playing on a two-monitor setup and I want to see something on the other monitor too. Playing a fullscreen game on one monitor makes the other monitor go haywire, with everything being shifted to the side a bit, and sometimes colors being all wrong on that second monitor. None of those problems if I run the game in a window instead, I can then also decide more easily on which monitor the game runs, just move the window. In fullscreen mode it will always select the primary monitor, so I'd need to change graphics driver settings if I want to play it on the other monitor instead. Other than that, only fullscreen.
Yesterday I came across a program that is sold on Steam that deals with this issue.
/ You should check it out.