Buying Laptop in Japan

I am planning to buy laptop in either Osaka or Tokyo and I am not sure which computer store I should go to with best prices and English speaking staff.

Where should I go?

laptop computers in stores are Japanese Edition and not English Edition.

I suggest you do some research first. Besides the aforementioned Japanese OS, Japanese laptops are outfitted with Japanese keyboards. With some exceptions, neither are easily changed out to English.

English editions are available but tend to be expensive. Plus you should do some price checking as laptops are generally expensive in Japan. You can compare your local prices to what's available on Amazon.co.jp and Kakaku.com

Yeah, most laptops over there have japanese OS and Keyboard... One notable exception is Apple, which will let you choose your keyboard language when you buy through an Apple Store.
If you don't do Macs, then don't bother with it.
Just my 2c

I would recommend a shop that has English speaking staff and cheap prices, this would be best for you if you wanted to buy one in Japan...

I looked on kakaku.com and the prices are a lot lower, besides they have latest models and 4th generation latest processors that are not available outside of Japan. Is it hard to change the keyboard and os to English? Are there any good shops in either Tokyo or Osaka that can set it up?

Its hard to generalize. Can you let us know what specific models you have in mind?

I was looking at these models:
GALLERIA VF-HG K130927
Critea VF-HG K130910
Dynabook Satellite T874/87K
Dynabook Satellite T574/55K

Is it hard to change the keyboard and os to English?

For the keyboard you'll have to check if its a user replaceable part (doesn't look like it) and if there is a au version drop in replacement that you could buy.

The OS is a little easier especially if you get windows 8. There's instructions here:

http://www.makeuseof.com/tag/how-to-change-the-system-language-in-wind...

If you get windows 7 then make sure you get ultimate edition. Otherwise it will be much harder to change the system language later.

Lenovo lets you select an English OS and US keyboard with no extra charge.

GALLERIA VF-HG K130927
Critea VF-HG K130910
these are DOSPARA original model.
you need to go to DOSPARA stores or their homepages.

Dynabook Satellite T874/87K
Dynabook Satellite T574/55K
these two are TOSHIBA direct original model.
only selling in TOSHIBA direct homepage.

Are DOSPARA stores good? I found one in Akihabara Tokyo and Namba Osaka, both within minutes from where I'll be staying.