I noticed XFree86 recently released version 4.5.0. I was under the impression that XFree86 was no longer being maintained and that X.org would replace it. I am currently using XFree86 4.4.0. Should I upgrade to XFree86 4.5 or go with X.org? I have an NVidia card, do the NVidia drivers support X.org?

Yep I have Mandrake10.1 with Xorg (not sure of the version) and the nvidia drivers/hardware accelerators work great.
Followed the instructions provided by nvidia easy to do.

Xorg is a "fork" of Xfree86. Basically they both originated from the same source code. Both forks are developed. I beleive the fork was due to licensing issues. And for the most part they are still compatible. Although I'm sure there are deviations and extensions, etc.

That being said, I remember reading that Redhat normally puts some extra work into their xserver, so I'd recommend Xorg. However for all basic intents and purposes I doubt you would see any major difference unless you have a card with some recent support added/changed etc.

Almost all nvidia cards are compatible with both Xorg and Xfree86. The nvidia driver should work on both.

oh no this isn't correct at all
i'm constantly amazed at how in the dark Linux people are over the history of the x server
while generally Tuxers are fairly aware of this type of stuff

first let me apologize for the length but people can read it or not.

XFree became a sort of part of Xorg in 1999 with a voting seat on the board
at the present time changes to XFree go into the cue for for review and implementation into xorg

Xorg is a huge ungodly unLinux collaberation between big buisness and other big buisness and ex MITers and their cunsulting firm and whatnot and is pay big bucks for a chance to play and has been around for a long time making its first commercial release in 1986
Compaq Computer Corporation (NYSE: "CPQ"), Hewlett-Packard Company (NYSE: "HWP"), Hummingbird Communications Ltd. (NASDAQ: "HUMCF"), International Business Machines Corporation (NYSE: "IBM"), SGI (NYSE: "SGI") and Sun Microsystems Inc. (NASDAQ 100: "SUNW") Metro Link a company that writes software for Space Shuttle, Crusader Howitzer, Army Land Warrior yuck yuck yuck
even at one point xorg and i imagine still taking big bucks directly from the US Pentagon
US taxpayer money in your Linbox (free as in free to kill everyone on the planet)

XFree came after Xorg and was based originally on The MIT X consortium Intel X server code
1991/92 it was early on a comercial product called X386 now XiGraphics AcceleratedX.
XFree forked from that to stay well -- FREE and XFree86 inherited the MIT license.
XFree86 freely merged it's code back into commercial MIT X11R6 just as they now do with Xorg.
XFree also benifitted from code from comercial companies it shared with contributing code back to it.
the Open Group took over from The MIT X consortium. the Open Group was pay for play like x org and at X11R6.4 they went closed source. XFree86 carefully backed out all the merged Open Group code and continued on its own and it was that decision that gave Linux an x server -- without that decision there would have been no RedHat or any of the rest of it. Open Group later abandoned it's restrictive liscense and code remerged.
XFree had to suffer alot of big companies breathing down their necks and reviewing their code for "secrets" and crap. Xfree did alot of work with hardware vendors getting them to allow open source drivers. and XFree obviously made major contributions with XFree4 to the architecture of X.

now here is the thing Xorg is the MIT X consortium/Open Group -- note the version X11R6.8.2
the same numbering system as Open Group
jan 2004 Xorg suposedly reconstituted itself or some crap turned over a new leaf or whatever
so i'm not trying to say it's a bad thing cause i don't know but it's certainly not Linux like XFree is.

Hmmm ... if you read here:
http://freedesktop.org/Software/xorg

It says:

Is that not a fork?

As clarification I was under the impression the OP meant Xorg that is currently distributed with Fedora and many other distributions.

Looks like a fork to me. foo_bar_foo clearly needs to swot up on his cutlery.

Its definitely a fork because earlier versions were based on xfree86 4.4 beta code.

from http://freedesktop.org/wiki/Software_2fXOrgRepository

The vendor branch has been merged to -CURRENT. -CURRENT also contains many other bug fixes and enhancements beyond what is in XFree86 4.4

When the community agrees, the -CURRENT branch is merged to the -STABLE branch

many OTHER enhancements
where did they come from ????
answer Xorg
it's just a mixture of XFree and MIT X which is what it has always been

there is of course a new level of propaganda thrown in to confuse everyone into thinking it's a fork
to maintain a pure liscense

the site starts off
The XOrg Foundation, (a.k.a. X.org) has changed to an Open Source model to maintain the official Public Implementation of X11.

and we are suposed to think they just took all the code they have been working on for the last
20 years and put it in the garbage ?

just wanted to add this to clarify
this is from
-Alan Coopersmith- alan.coopersmith@sun.com
Sun Microsystems, Inc. - X Window System Engineering