cant switch from X (gnome) to console using ctrl + alt + Fx, screen turns black
 

I cant switch from X (gnome) to console using ctrl + alt + Fx, The screen turns black

although i am able to switch back to X using Alt + F7. I am using Nvidia n6200 on Ubunto 7.10. I think the problem might be my xorg.conf which says my card is vanta as follows

Section "Device"
Identifier "nVidia Corporation NV6 [Vanta/Vanta LT]"
Driver "nvidia"
Busid "PCI:1:0:0"
EndSection

one more thing, when I run nexuiz on linux it does only 15 to 30 fps. but on windows xp it does 60 fps.

is X configured correctly???

Well, the "Identifier" line doesn't matter at all. It's just a line that sort of marks a certain device section, so in other sections you can refer to that certain device by that name. If you like, you can switch it to "MyAwesomeCard", but just make sure you replace it everywhere the same way.

nvidia is the correct driver - it's the proprietary driver. If you'd like, you can change that to "nv" for a while (you need to restart X - press CTRL+ALT+BACKSPACE) -- it's the non-proprietary/non-accelarated driver -- and see if you can then switch consoles better or not. Compiz won't run then, though, but you'll get it back when you change the driver back to "nvidia" again.

The FPS depends a little on what you do, I guess. The driver should be perfectly capable of doing at least the same than on Windows, at least I've noticed that here, so maybe you'll want to play around with it a little..you know, there's an "nvidia control panel" available too, for Ubuntu you can find it in the usual reposities trough Synaptic. See if there's something you can change. Or xorg.conf.

EDIT: try running
for a while. That should print some fps numbers..on my low-end card I get around 6500fps when it's running in the ordinary small window, and about 500fps when resizing the window to fill the desktop as much as it can.

no .... after changing the driver to "nv" the i still cant switch to console. instead i get a red/garbled screen.

glx gears give me 265 fps in small window, and with full screen it gives me 135 fps. thats way too slower than ur 500 fps.