Well, for starters, we need to make sure you know all of the specs of your video environment, namely, video card and monitor sync/refresh rates. This is required (obviously) in order to configure X.
Next, what method are you configuring X? Either way, can you post your XF86Config file (if you can, remove all lines commented out)?
You need to first get X up and running before even attempting to get kde up and running, but you probably already know this...