If you're using integrated graphics, then you'll have to check your exact adapter and driver version (probably something like a GMA 4500 or whatever with some old Intel driver) to be sure of what graphics adapter you have.
Also, since it is a CRT display, this shouldn't be too surprising. Unlike LCDs, Plasmas, and other flat screen displays, CRTs do not have native resolutions. Whatever the driver lets you run will usually run on a CRT so long as it can handle it. For example, I have two old CRT displays designed for 1024x768, yet they handle 1600x1200 without any issues, granted refresh rate isn't perfect when forced to use resolutions that are too high.