Greetings in a business email?

Hello, I need to send a business email to a client in Tokyo . Most of the message will be in English as my Japanese is not good enough, but I'd like to include an appropriate comment/greeting at the start and end of the message in Japanese. Should I comment on the weather as in a letter or do different rules apply for email? (In English I think the language used in emails tends to be a lot more informal, even in business situations). I'd be very grateful for some advice.

First comes the name of the reciever, of course (Dear --- or --- sama).

Then start with
Osewa ni natte orimasu.
お世話になっております。

And end with
Yoroshiku onegaishimasu.
よろしくお願いします。

before you sign your name.

"Should I comment on the weather as in a letter"

Basically, no.

"or do different rules apply for email?"

Basically, yes.

That's great, thanks very much for your help Uco.

Hi, I need to send a business related email inquiry to a company located in Japan. I found out the following post with regards on how to start and end the business email. http://www.japan-guide.com/forum/quereadisplay.html?0+20355

However, I am not sure how I should start with addressing someone if I do not know anyone working in the company?

There is a way to address the company (or the department in a company) without knowing the name. It will be like "Dear Sir/Madam of company A)."

If you have the name of the company, for example, ABC Co., Ltd　ABC株式会社 (ABC kabushiki gaisha), then you write:

ABC株式会社 御中
ABC Kabushiki gaisha onchu

Or if you also know the department (normally referred to as "... bu") name in that company, you could say:
ABC株式会社　XYZ部　御中
ABC Kabushiki gaisha, XYZ Bu onchu

Thanks AK. Thanks for you help.