I am not sure exactly what the person meant.
You can run DVI @ 1920x1200 (which I am doing currently on my monitor).
*BUT* HDMI (or) DVI-D is needed to watch certain HD content, because of copy protection.
For example, my PS3 won't work on my DGM 24" over a HDMI->DVI converter because it is only DVI and not DVI-D. On the other hand my 20" dell runs it fine using a HDMI->DVI-D converter.
Bottom line, for gaming then 1920x1200 on any screen is fine, even VGA should be ok (I am running 1920x1080 on m 360 over VGA).
1920x1080 is 1080P. This is more common on 16:9 screens, and 1920x1200 is for 16:10 (which most PC monitors are).
The only thing to remember though, if your screen doesn't have HDMI *OR* DVI-D, if you want to watch blu-ray for example it won't work, because of copy right issues. I think that should have answered your question - feel free to let us know if there is anything not clear
