Have the same problem on i386 Ubuntu 9.10 on machine with:
00:12.0 VGA compatible controller: nVidia Corporation C68 [GeForce 7050 PV / nForce 630a] (rev a2)

lspci -n
00:12.0 0300: 10de:053b (rev a2)

This is integrated graphic chip on ASrock 939N68PV-GLAN. I'm using VGA output.

After booting from Install CD into "Testing Ubntu befor install", i see bootscreen with progress ok. Then X server lanchues, and my LCD (Samsung SyncMaster 710v) goes crazy it displays some green lines and some pattern in squares which filicrs. It mainly consists of green, yellow and blinking red vertical lines of 1 or 3 pixels wide. My monitor also shows diagnostic box that Not Optimum Mode, Recommended Mode : 1280x1024 60Hz. After one minute screen goes blank to save energy (even if i move mouse, etc), and becuase mode is inproper.  Moving mouse or pressing Alt-F2 doesn't chang any pixel (beyond stil blinking) on the screen.

But keyboard works, Alt-F2 does something (i hear CD spinning), and Ctrl-Alt-F1 switches me to the Linux console. (then i can be back by Alt-F7 exactly like on the begning).

Text mode is also broken in Linux console. it is in 80x25 real text mode (no fb), displays text correctly in proper color et al, but cursor (small bar) is blinking always at the upper left corner of the screen (first character of console).

Shift-PageUp/PageDown doesn't work. "clear" and "reset" works, they clear screen and puts prompt at the top. But they put this prompt on the second line sometimes (in if when it was clearning i will press additional enter)! In first line I still see some text from before the clear/reset. If i now switch to Alt-F2 and then back Alt-F1, first line will dissapear and will be empty or empty prompt. But I still will be writing in the second.

When i hit bottom of the screen, console doesn't scroll. So i effectivelly doesn't see what I type also. Even if i hit enter 200 times, it will not scroll (so it is not thinking that i have 50 line screen).  BUT when i will switch Alt-F2 and then Alt-F2 screen is correctly redrawed and i see what i was typing bellow the screen.

Somtimes there are other strange behaviours with scrolling (or more appropriate not scrolling but cycling again from the begining somehow), but it is quite reare and can't find exact pattern (it happend when i keep pressing enter for longer time an from time to time ener some other text, of course not seeing this).

What is also interesting is that when I perform cat /var/log/Xorg.0.log screen scrolls somehow! There is also some situations when screen scrolls (or more appropriatly it instantly switches to new state, without scrolling, when i keep typing bellow visible screen, and then stop). Some really strange timing issues probably. 'more' command isn't working very well (but after PgDown, switch to F2 and then to F1, it is ussable to view some files).

PS. I have also "cx88 IR (AverTB Studio 303 M12" Radio/TV tunner which is correctly detected by X.

BTW. Screen corruption isn't exactly like on the http://launchpadlibrarian.net/35284915/screen-corruption.jpg (on this image there are square structure, which my problem lacks, only vertical lines + few other pixels).

"Safe mode" F4 works perfectly ok for installation or testing.

Hopes it will help.