I was having trouble locking the screen resolution of Fedora as it ran under VMware Fusion on my MacBook Pro 2.33Ghz Intel Core 2 Duo. Initially, I set the screen resolution using Administration -> Display. For a reason unknown to me, setting the resolution of 1440x900 always reverted to 1680x1000. Playing around for a half an hour, I finally figured out that Display was not going to work. I then used Preferences -> Screen Resolution:
This widget successfully set my Fedora Core 6 desktop resolution to the exact screen size of my MacBook, a lovely widescreen 1440x900.