OK im looking to upgrade some parts on my PC.

Specs are as follows:

Operating system: Microsoft Windows XP Media Edition
CPU type: Intel® Core™2 Quad CPU @ 2.40GHz Q660.
motherboard: Asus P5N-E SLI.
RAM: 4 GB
Video card: ATI Radeon HD 2600 XT (Resolution: 1024x768x32)
Disk drive: Model ST3250824AS (Size: 232.9GB)
Disk drive: Model WDC WD5000AAKS-00YGA0 (Size: 465.8GB)
Optical drive: PIONEER DVD-RW DVR-108
Case & PSU: Thermaltake case(unknown exactly) and Thermaltake 430W PSU.

Parts im upgrading toare as follows:

(ignore the peripherals, its a copy and past from another forum)

Logitech G15: $119
LG DVD22X+- DUAL LAYER DVD Rewriter with Software(GH22NP20) : $39
Xigmatek CPU Cooler S1283 Red Scorpion : $53
SeaSonic M12 600W Modulate PSU : $164
Razer Lachesis 4000dpi Razer Precision 3G Blue Laser Mouse USB2.0: $119
MSI nVidia GTX 275.

The part im not sure about is the GTX 275. I cant find out if its compatible with the P5N-E SLI.(and everything else to be exact). Anyone have any idea? or need a link to said parts?

Also, any advice/comments on weather or not these parts will be a good upgrade?

it sure is, you can also stick 2 X GTX 275 in that mother board. If you can pick up a Corsair HX-620, quiet and reliable, not sure about the Seasonic.
G15 Keyboard is good, got one my self.

Ive been thinking about running two but i thought it might be abit overkill? computer is used mainly for gaming. Such as Battlefield 2, CS 1.6 CS:S, WoW and so on. Also random web surfing and download ect. Im using a 32"LCD TV as a monitor however, would 2 cards have any effect on this? be it good or bad?

All 4 of those games you should get decent/excellent FPS with one GTX 275. What resolution is the 32inch running at? I'd stick to one card and when you actually need the second one get it later on when prices have dropped or when you want to play a more gpu demanding game. or you can just wait for the DX 11 card's instead of buying another GTX 275

As for screen resolution, what do you think i should run it at?

Depends on your monitor, most 22inchs are 1680 x 1050 (1200 for widescreen) and 24inch 1920x1080(1200 for widescreen).
Just whatever suits you lol basically

I've got a gtx 285 in my new comp, fucking awesome

Running two cards in sli mode is actually worth it these days with new tech and drivers. When it made it's come back 4 years ago, you only got a few extra frames and was just a waste of money. Saving up some money for another card down the line can give you a nice boost for future games or max graphics on new games.

1 gtx 275 will run all those games on a 1680x1050 res screen, full graphics. But if you ever want to sli 2 cards, you will want to get more then a 600wat psu, more 800~ range
Is there a reason you want to switch from radeon to nvidia?

And Pioneer also make great dvd drives. The Pioneer DVR-217BK is awesome, but it's only 20x.