My Dell 24inch WS (2405fpw) displays games like Diablo 2 in the regular 4:3 mode with black bars on the side. I can't remember but I think it's my vid card that does the conversion (6800gt).
I would SOOOO not use an LCD for vintage gaming. Non native resolutions look like utter crap. Just get a decent 19inch CRT for peanuts and you'll be set 😁
Oh and one last thing, if you go widescreen, don't go for anything less than a 24!
I went from a 19 CRT to a 20.1 WS and it just wasn't doing it for me, definately didn't have the 'wow' factor cause it was basically the same visible height as the 19.
Check out places like slick deals and you can get a 24er for ~600 or less (I got mine for $412 back in the day on a steal of a deal)
Dell Optiplex Gxpro: Built solely so I could re-live my SB16 days properly with newly acquired sound pieces: MT-32, SCB-55, and DB50xg 😀