I don't even have to do that on my work PC. Just in the normal Windows display settings, click on the display you want to change, and change the resolution. You'll see the two display representations change size to represent their relative resolutions. If you want to set the refresh on each one, click the one you want, click Advanced, and set the resolution, then do the same thing for the other one (you can't choose which one to set from the Advanced tab).
Oh, and on the display optins, there's a checkbox for "make this monitor my primary display or something to that effect. Whichever one shows as number 1 is your primary. This actually changes which port on your video card (or which card if you have more than one) is treated as primary. I think you can also just drag the #2 display to the proper location, which leaves the port settings alone.
In the Windows Help system, do a search for "dual monitor". All this and more is explained.