wasn't sure how to word this question. My desktop runs at 1920x1080 resolution, and just from the sharpness of the screen and the graphical behavior, I know that the graphics card is working fine and the resolution is correct.
But everything looks huge. my taskbar and desktop icons are about the only thing that looks the right size. Windows open as huge boxes that clog half the screen, the KDE application menu (whatever you call the thing that pops up when you click the K) goes to the top of the screen and 1/3 of the way across it. You get the idea.

I know on other distros I've used (Mandriva, Slackware), the windows were the proper size, but for me they look like they're running at 800x600 or 1080x768.

Anything I can do to fix this?

Did you tried reconfiguring the KDM. I'm not using KDM. I had some thing similar with GDM. What I did was stoped the GDM and reconfigured the xserver. hope this helps

Kde systemsettings > Appearance":

there is a menu to force the DPI's (bewteen 96 and 120)


Open Konsole and check your resolution:

xdpyinfo | grep dimension

This will tell you what the actual resolution of X is on your desktop. Next, look at the DPI setting.

xdpyinfo | grep resolution



Xorg - ArchWiki
http://wiki.archlinux.org/index.php/...y_Size_and_DPI

1920x1080 pixels, 341x191 mm

143x144 dots per inch

Is that a normal-looking setting or should it be changed?