I am having the following configuration

AMD64 X2 3600+
ASUS M2NPV-VM motherboard (NVIDIA GeForce chipset)
DDR2 1 GB RAM
160GB SATA Harddisk

After installing the Fedora 6, am able to login in GUI mode and able to choose KDE & GNOME in 800x600 resolution.

So I have downloaded the latest NVIDIA display driver for AMD64 and installed.

Here am facing different problem. The Fedora loads with GUI. After the services are started, the console login screen is appearing. It is not opening the GUI based login screen.

To see the X windows and GNOME, I need to
1) login in console
2) delete the file /tmp/.X0.
3) start the x server by startx

I verified the runlevel, it is 5 only. The log /var/log/Xorg.log is also fine. Actualy the xserver is started in display 0, but after that it is showing console. The services startup status is shown in xwindows mode only.

How I can make the default X windows based login?

Hello and welcome. It's been awhile sense I've been back here and I try to help when I can. Maby this could help you http://www.tuxfiles.org/linuxhelp/xbootup.html It helped me.