screen resolution

I' ve got a new 24'' iMac which I love,but I'm not happy with the screen resolution. If I go to screen properties, I see that my current settings are 1920 X 1200, which makes very little letters in most applications, not too good for my poor sight. The previous resolution is 1344 X 840, which is extremely big, even for me. I have seen in the 20'' iMac that it has an intermediate one, 1680 X 1050, which would be perfect for me. Is there any way to get this kind of resolution available for my iMac?

Thanks in advance.

I have no dealing with the 24" iMac. I thought Apple used the 16:10 format for all of their monitors so 1680x1050 should be a selectable resolution. If it's not, I don't know how to help.
If you hold the far bottom oft key down on your keyboard you can zoom in and out with the little click button/ wheel on the mouse.
If you are using Safari, there should be a preference to let you make the text larger.

There's several suggestions in this page:
http://macosx.com/tech-support/mac/how-to-increas-default-os-xapp-font-sizes/3190.html

One app to try is TinkerTool... it will let you change the size of several system fonts.

Also... in the Displays Preference Pane, click on "Detect Displays" and see if that gives you more resolution options.

Ideally, you should stick to the "native" resolution for your monitor since anything else will lead to blurry fonts. Instead... try increasing the font sizes. You can fix many using TinkerTool for the system, but many apps will require you to set the new font size via their own preferences.