Planning to build a mining rig im new to the digital currency scene. Im very interested in bitcoins and litecoins. I know about bitcoins a couple of months ago and how foolish of me not to invest in it.

Anyways, im interested in litecoins now as they are really easier to mine and they can also be mined using the CPU which on my computer is probably the best thing. this is my setup:
AMD Phenom II X2 550 3.1GHz (unlocked the 2 cores so bascially a quad core at 3.1Ghz).
4GB RAM
9800GT 

Im actually thinking of setting up a litecoin rig, which has 2x 7850's but im really unsure about how much power that will use and what power supply i should buy (e.g. 600W or a 700W etc). Ive seen some videos on youtube about mining using the 7850 and this guy was mining using 2 7850's and he total power was about 850W which is pretty crazy (he did overclock and things like that). Im planning to mine on stock hardware meaning no overclocking so how much power in total do you guys think that will take?

But now i guess the news has gotten around about a ASIC litecoin mining machine coming up so no doubt the value of litecoins will increase and i want to take advantage of this situation. 

So should I go for that rig with 2x 7850's or is there a better rig I can come up with that will use less power? (My budget is about £400. This includes the power supply, cpu, ram etc). Also, would it be better if I just buy the litecoins directly rather than mining them?

I also used this litecoin calculator to see whether I would be getting a profit/loss:
http://www.coinwarz.com/calculators/litecoin-mining-calculator/?h=650&amp;p=450.00&amp;pc=0.26&amp;pf=0.00&amp;d=2218.89256388&amp;r=50.00000000&amp;er=0.03408000&amp;hc=0.00
I used the 650KH/s since I assumed at stock 7850, it would give about ~325KH/s. Since the gpu uses about 120W, i got the 450W from 2 7850s, the cpu, and some other electrical components (e.g. RAM, HDD etc). Since I live in the UK, the average price per kWh is 16p so thats ~$0.26.
What I dont understand is that on the summary where it says 'Days to generate one block mining solo: 169.69 days'. What does this actaully mean because bitcoins are harder to mine compared to litecoin but on that calculator, it says i'll mine a bitcoin in 99.59 days...

Also, where it says estimated expected earning, it says i'll generate  ~8 litecoins in a month but previously it said that I'll only be able to mine 1 litecoin in 169.69 days... Is this talking about mining in pools?
169.69 days you will get solo reward (keep in mind that it is not guranted, so it could take more days), I`m not sure how much it is now, e.g. in bitcoins now you get 25BTC for success solo mining. Earning table, that you see, definitly talking about mining pool.