1.It weighs about a pound.

"about" is a preposition here.

No, it's an adverb, an intensifier for the noun phrase, 'a (=one) pound'. (Quirk, Greenbaum et. al. 7.62)
Students: We have free audio pronunciation exercises.

How can I get the book youhave mentioned written by "Quirk, Greenbaum ".

I am from India. Is this book available in India?

Thanks a lot for your quick and thoughtful answers.
It's not available in Japan, Hanuman-- but with the internet, I can and do order books from everywhere.

A Comprehensive Grammar of the English Language, Quirk, Greenbaum, Leech & Svartnik (Longman 1985), ISBN 0-582-51734-6, is quite expensive.

A Student's Grammar of the English Language, Greenbaum & Quirk (Longman 1990), ISBN 0-582-05971-2, is a paperback, shortened version of 'A Comprehensive Grammar'. It lacks many of the examples, but is very much cheaper.

New books can be searched at Amazon.com, but these may be out of print. Used books can be located via such sites as [url="http://www.abebooks.com /"]Abe Books[/url] or [url="http://www.addall.com /"]Add All[/url].