Here is a copy of the bug reports at Bugzilla, I copied it entirely to show how many people are experiencing same or similar problems.
URL: http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=18810

Corrupt display = snow, flickering artefacts around characters in text mode and flickering horisontal lines around the screen objects in X.

First, I am unable to install in graphics mode: screen is badly corrupt,
no GUI controls visible. Setup is able to run but it's impossible to
operate it.
Text mode setup of XFree86 recognizes Voodoo banshee and installs. When
trying to run X aftewards, I am experiencing a number of bugs:

1. Corrupt display: GUI controls invisible, only bitmaps displayed
correctly. Window border exists but not window content and not window
buttons.
2. Switching resolution occurs but the next 10-15 seconds computer does
not responds and finally hangs. No response to Ctrl-Alt-BkSpace.
3. X can even hang unpredictably upon startup.

The bug was first experienced in RedHat 6.1, reported in 6.2 and never
fixed. In fact I am unable to run X at all that's why high prioirity and
high severity.
------- Additional comments from vader21@imsa.edu 2000-10-19 04:52 -------
If you have a Creative Labs 3D Blaster Banshee AGP, there are some issues
between the hardware (specifically the SGRAM) and the driver. There are working
drivers on http://linux.3dfx.com/ but you cannot use the drivers there that are
based on XFree86-4.x. The modifications that these drivers incorporate have not
been incorporated back into XFree86 for whatever reason. If this is indeed the
problem that you are having and would like some help in setting up the drivers
from linux.3dfx.com since there aren't any instructions there for redhat-7.0
send me an email and I would be glad to help.
------- Additional comments from alex.im@usa.net 2000-10-20 12:19 -------
No, that was not Creative 3d blaster:
Video board is ASUS AGP-V3200 with 16 MB SGRAM.
CPU: Intel Celeron 333 at 300-333 MHz.
ACorp 440LX motherboard. 64 MB PC100 RAM.
------- Additional comments from arch0nemesis@optushome.com.au 2000-10-22 03:57 -------
I too have had this problem on my Banshee's since RH 6.1 and have tried most of
the custom X servers (3dfx and Creative drivers/servers) and none of them fixed
the random resolution changes... XFree86 4.0.1 does not fix the bug and the
bug also appears in UniX (as the bug is in the XFree86 server).

The problem is "not" limited to the creative cards as some report, it appears
that many of the generic cards have this problem.

Unfortunatly this bug prevents the user from entering X at all..... this is a
high priority bug and i look forward to its fix....

My system specs:
-----------
Skywell and STB AGP Banshee
Celeron 400
Kernel 2.2.17
XFree86 3.3.6 (also tried 4.0.1, 3.3.6, and Creative/3dfx servers)
-----------

------- Additional comments from tristan@optushome.com.au 2000-10-22 04:52 -------
From what i can figure out the bug is in the XFree86 drivers because now that i
have changed over to freebsd i still have the problem it seem to affect the
video modes dose all sorts of things from shake video at hi rez of
1280x1024/70hz and i know its not the card of my monitor or vidcard because it
works fine in Windows 2000 at that and higher rez. I think that the Severity of
this bug is very high and will affect lots of new Redhat users and should be
fixed a.s.a.p seeing that it has been a problem since Redhat 6.1 and so that
people with a Banshee can enjoy Linux/Unix beyond the console. I have also
experanced some of the problems of the other bug reporters.

My System
|-------------------------------------------------------|
|Lightspeed 3300 STB AGP Banshee |
|P3 500 Running at 560Mhz 112Mhz FSB |
|256Mb Ram |
|Abit BH6 MB |
|Was running Redhat 6.2 now using FreeBsd 4.1.1 Stable |
|XFree86 4.0.1 using the tdfx driver |
|-------------------------------------------------------|

THX Tristan
------- Additional comments from arch0nemesis@optushome.com.au 2000-10-23 03:23 -------
After more testing and upgrading kernels to 2.4 test 9 i have discovered that
when the bug occurs (resolution incorrect/invalid) if one kills the X server
CTRL+ALT+BACKSPACE and is returned to the console (screen does not return
however, all is black) and one tries to re-enter X all returns to a working
state (screen comes back from state of blackness).....

This is interesting in that the banshee can be recovered -previously untested (i
think)- and shows that the X server must place the banshee in an incorrect
mode/state which causes the card to hang..... However if the X server is
reinitialised the screen returns from a state of darkness (however the error
randomly reoccurs and one must repeat this step).

I hope this helps people to correct the bug..... -n3m3sis