The SSD is optional, it's just another storage device. It performs much faster than a HDD though.
@Paradox
This is a nice build, but I suggest taking a 3570K, it doesn't cost much more than the 2500K (at least not in Croatia).
The GTX 570 also offers by far better performance than the 560 Ti, even though it does a few extra dollars.
The SSD is to install applications/games on it, it's like a nexternal HDD or something, I've never actually used it.
I also suggest buying a cooler.
If you can expand your budget anyhow, make sure to change that 620W into 700W, in case you buy and extra GPU or something later.
It's a great looking build for the cost... I would of gone with the Caviar Black over the Caviar Blue... Buy an After Market CPU Cooler over the standard one & some Arctic Silver Thermal Paste...
Honestly, who pays for their operating system...
I suggest you get a full tower case.
Looks like you kinda just threw it all in there, look up reviews for better quality in all parts.
Don't buy the Windows 7 CD you can get one from a torrent and burn it yourself.
Full tower case and just take the 1tb harddrive..
Skip the OS and upgrade to a Z77 mobo and a 3550 cpu. Chances are you won't ever OC.
the ssd thing is optional, but I suggest you buy one (preferably a sata 3 one)
I have a 64GB sata2 kingston SSD, and I love it, and it was well worth the money
Usually you install the OS on the SSD and Games. I recommend a corsair 128GB; 40gb for windows and extra space for hard hitting games like Crysis and skyrim.
It will make windows perform ALLLOT FASTER and the GAMES START FASTER AND RUN NICER!