My friend has an Xbox 360 and hes saying that Call of Duty 4 has much better graphics on XBox than pc in 1920X1080 resolution. Is this true?

Nope!

Not necessarily..
If a video card could output to full HD resolution, but with no filters, shading etc. then the 360 would look better.
You'd need a card capable of outputting to full HD, with say 4x AA (I'd guess thats probably along the lines of what the 360 runs, but it is just an educated guess...) all the effects and at a solid 40fps? I don't know what the target fps for the 360 is, but again just an educated guess at 40fps.
To do that on a CPU, I'd imagine you're looking at 3870 minimum, so not quite as clear cut as "Nope!"

Haven't this been discussed already on this board?
 
The question didn't specify what pc we are talking about so i imagine were not talking about the cheapest dell now.
 
YES, not all pc will be better but also NO, the highend pc's will far surpass the 360 or something like that.
 
So "nope!" is a perfectly valid answer i think. =)
Correct me all of you who own both and can compare them.
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Maybe is the correct answer since we don't know the pc specs.
 
But you could always crank the graphics up and play a slideshow with a PC, so it's a yes to the PC can make it "prettier" .
 
ps cod4 on consoles = 600p.

Having seen both on my 1080p LCD I can say without a doubt that the PC version looks better. COD4 on my 360 looks incredibly blurry in comparison; not surprising considering that the 360 is upscaling a <720p image to 1080p while my PC is outputting true 1080p with 4xAA.

I haven't played either console version yet (nephew has 360 version), so can't comment first hand.  
 
ANyone know if the 360 version uses any level of Aniso or is it left out like Oblivion?  Without AF it will never look as good as a decent PC IMO.  Plus by 4xaa and HD, they are refering to 720P and 4xaa right?  1280x720 4xaa would be quite easy settings for current $150 and up.  
 
And from what I have read, the console versions both run 2xaa in this game and at 1024x600p  res.  
 
LOL, ya beat me to it.

on the xbox it uses 2xAA, don't know anything about AF settings.

There's no doubt about it. Using a PC that can play it at 720p or above is going to going look a lot better than the Xbox. It's only 600p and when it's hooked up to a 1080p TV, it's upscaling the image, which as anyone who has watched an upscaled DVD versus 1080p Blu-ray knows the difference.  
 
That being said, another great thing about the PC version is the ability to download new maps and mods, which really extends the life of the game considering that it' sooooooooo short and the maps are very small and linear. I'd take the PC version over the Xbox version any day of the week because of this fact, even if I only had something like a 7600GS. Just take a look at TF2. It's so much better on the PC because of all the custom maps. Xbox is stuck with the original few. The custom maps introduce a whole new level of gameplay and most make the scout a lot more playable (my favorite class.)

HANDS DOWN at 1920 x 1200 with 4x aa and 8x af on and no jaggies,PC has the 360 beat by a mile!
 

We have 360s in my house and I can tell you without a doubt my computer has a better quality image. I run max settings @ 1920 X 1200. The only problem is we do not have any 1080p TVs to do a proper benchmark, but I seriously doubt they could be on par.

Who cares, just enjoy the game.

No Tv not even current HD ones have a native resolutions equal or similar of the Widescreen Monitor. So even if it does have x2 AA it's still barely enough to keep up with the average gamers PC screen's clarity.  
 
If you force the screen into HD mode then yes i agree it would be a fair test, but 1280x720 is what most TV's run at natively and as far as i know the bigger the TV screen the bigger the pixel's because it doesn't support higher resolutions. So therefore the x2 AA is required to have a half decent image display.
 
As for the graphical hardware behind the image thats different again however, most people on this forum have an ATI x1900/1950 equivalent or higher so can run CoD 4 pretty much max'ed as it is with 35+ FPS.  
 
I've seen my m8's and they've seen mine and they definitely say they would prefer playing on my PC than on the 360.

Actually most flat panel TV sets we call 720P are 1366x768 native res, so scaling occurs anyway.  Front/rear Projectors are often 1280x720 native.

 
Full HD native resolution (generally on TV's of 42" or larger) is 1920x1080 and as long as it is 1080P, that's fully progressive. For that resolution on a monitor, you'd need at least a 24" (I believe Acer make a 24" 1900x1200 monitor), although more likely a 27" or greater. I don't know anyone who games at 24" or higher, so most don't game at a resolution close to Full HD.
Although I know the 360 can only output at 1080i, the PS3 can run 1080p can it not?

All 24" WS LCD Monitors are 19x12 native AFAIK.  And remember, In the case of COD4, as was mentioned many times above, it's a 1024x600 pixel count and scaling to 1080i or p on both the PS3 and 360.  

*edit* Damn you, Pauldh! Beat me to it.

Any 24" widescreen monitor should be 1920x1200. Larger than that starts to become 2056x1600 (I think that's right).

Although it can output 1080i (maybe 1080p) I believe that it is all upscaling, and not true HD. Also, most games on the PS3 and XBOX only transmit in the 1280x720 resolution and are stretched or "upscaled" to fit the screen. There is a loss of quality in this conversion.

It has already been said above, but I'll repeat it. A PC that is build with the right parts / displays will always come out on top in graphic quality / performance. If you take an 8600GT and try to run COD4 at very high @ 1920x1200, of course the XBOX is going to look better. That card probably can't generate a smooth enough frame-rate at that res.

 That happens to me alot.  You type out this big response, even look for links, submit, only to see someone tossed out a quick sentence and beat ya to it.