Well, I can answer most of your questions and I can show you what I just ordered (shipped today) for around the same budget with keyboard, mouse, & Win7 but I already had a decent monitor.
First up, Overclocking is the process of running a computer component (generally CPU, but can also include the RAM and video card) at a higher clock rate (more clock cycles per second) than it was designed for or was specified by the manufacturer, usually practiced by enthusiasts seeking an increase in the performance of their computers.
Second SLI: Scalable Link Interface (SLI) is a brand name for a multi-GPU solution developed by NVIDIA for linking two or more video cards together to produce a single output. SLI is an application of parallel processing for computer graphics, meant to increase the processing power available for graphics.
And Crossfire: AMD CrossFireX (also known as CrossFire) is a brand name for AMD Graphics Product Group' multi-GPU solution. The technology allows up to four GPUs to be used in a single computer to improve graphics performance.
Sum it up: SLI is Nvidia's solution to using multiple graphics cards and Crossfire is AMD's solution.
For the Budget, I would go with an SSD for OS and Main Programs
A solid-state drive (SSD) is a data storage device that uses solid-state memory to store persistent data with the intention of providing access in the same manner of a traditional block i/o hard disk drive. SSDs are distinguished from traditional hard disk drives (HDDs), which are electromechanical devices containing spinning disks and movable read/write heads. SSDs, in contrast, use microchips which retain data in non-volatile memory chips and contain no moving parts. Compared to electromechanical HDDs, SSDs are typically less susceptible to physical shock, silent, and have lower access time and latency. SSDs use the same interface as hard disk drives, thus easily replacing them in most applications.
And here is the system I ordered:
Qty. Product Description
1 ASUS P8P67 DELUXE (REV 3.0) ATX Intel Motherboard (You can also go with the new Z68 chipset, which allows SSD caching and video transcoding)
1 SAMSUNG Black Blu-ray Drive SATA Model SH-B123L/RSBP LightScribe Support (Retail)
1 EVGA SuperClocked GeForce GTX 570 (Fermi) HD 012-P3-1573-AR Video Card (Lifetime Warranty)
$354.99 (You can also go with the AMD 6970, performance is a few hairs different as is price, both cards support more than 1 monitor)
Microsoft Windows 7 Home Premium SP1 64-bit English 1-Pack
HD + PSU Combo
1 SAMSUNG Spinpoint F3 1TB 3.5" SATA 3.0Gb/s Internal Hard Drive -Bare Drive
Item #: N82E16822152185
1 CORSAIR HX Series CMPSU-850HX 850W Power Supply
Item #: N82E16817139011
RAM + CPU Combo
1 G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory
Item #: N82E16820231445
Thanks! That's actually better than whatever, I was expecting,
now, I'm probably going to run 2 monitors, only for extreme multi tasking,
also, i have 2000$ just to spend on the computer and its components itself,
I have the keyboard i want and mouse from old pc,
and i have a another budget for my monitors, as I want a 30-40" monitor for one, and a 20-25" as another one.
If you are planning on going with higher resolution than 1920 x 1080 and gaming, I would suggest going SLI or crossfire. Also, for both, they only work if all the monitors are running the same resolution. Even if only running one card to more than one monitor, they need to be the same resolution.
30-40inch monitors work fine in 1920 1080 res so there isn't much to worry about illSilver.
Just like what cyberaptor said above, if you are going dual monitor either SLI or go with a 2GB card like the 6970 from AMD.
The only thing I would change is the motherboard and SSD. The only reason to really pay over 200dollars for a motherboard is extra PCI-e cards for SLI/xfire options x16/x16 or x8/x8 and couple extra sata3, 3.0 USB ports. You can easily find a board that is 150 or under with the same performance as 200 dollar mobos. OF COURSE if you need extra slots and connectors then go with the 200dollars mobo, but it really doesn't seem like you need it looking at your system usage.
Also for the SSD I suggest looking at the new Corsair Force 3 which has a very impressive read/write speeds. I haven't looked at any reviews yet, but if the specs are running intended with low failure rates then I am probably going to grab one myself. The price is also cheaper then the OCZ 3.
Also for cooling, it doesn't really seem like you are going to try and overclock to the max potential so I suggest getting a cheaper air cpu cooler like the CM Hyper 212+. I currently have it pushing my 1090T at 4.2GHz with max temps hitting 57-60c on prime95. You can save another 50dollar on cooling that way.
With those couple shaving off the hardware you can probably get the dual monitor like the one cyberaptor posted at the 2k price range.