If your screen space is severely limited, e.g. if you’re running a sub-notebook, KDE2 will run just fine. I can work comfortably at 640x400. To make KDE work nicely, I just adjust the font and icon sizes via kcontrol,set kicker to ‘tiny’ mode, and use my ‘we’b styles for widgets and kwin, which are designed to work well at low resolutions.
Have a look at this screenshot: mini-kde.png to see how KDE looks at 640x400. Yes, I can work comfortably with multiple applications at this resolution. KDE is unique in the field of UNIX desktops in this regard.
I’m sure KDE will work fine at lower resolutions too, I just haven’t tried anything smaller than 640x400 yet, because I can’t be bothered to set up X11 to cope with smaller modes.
Note that I have not used the clearest font possible. The best font I have found for low resolutions is Verdana. I used a different font because Verdana is only clear at a slightly higher pixel size. I would likely use Verdana, taking the maximum amount of text on-screen down slightly, if I were to use this resolution on a regular basis.
I don’t actually own a notebook. If you want to send me one so that I have some incentive to make KDE work even better on a small screen, I won’t complain ;)