OK, so you found the solution to your first problem (using 'startx' instead of 'kde'). Now you would like to run this automatically after boot?
Edit /etc/initab:
Code:
# The default runlevel is defined here
id:5:initdefault:
Runlevel 3 is without graphical environment, 5 is with.
EDIT:
After reading your post the second time, I realised that you probably have runlevel 5 configured already. Do you really end at a black screen? Maybe if you wait the KDE login screen comes up?
Check /bood/grub/menu.lst for a suitable vga= setting. Maybe the resolution is set wrong for the framebuffer device.
Code:
| 640x480 800x600 1024x768 1280x1024
----+-------------------------------------
256 | 0x301 0x303 0x305 0x307
32k | 0x310 0x313 0x316 0x319
64k | 0x311 0x314 0x317 0x31A
16M | 0x312 0x315 0x318 0x31B