I need statistics to show that Hinduism is growing, both in the
East and the West. I need something which accounts for the rise of
global / regional / country population growth of Hindus.

Dear Golden Avatar, 

The question of the rise of Eastern religions in the West has several
explanations and quite frankly, my answer will probably not cover
every theory, given the fact that this issue has been dealt with the
numerous studies. Here are several recommendations:
* The Hindu Diaspora : Comparative Patterns by Steven Vertovec 
* Books that explore Hinduism in the West as a New Religious Movement,
like James Lewis' Encyclopaedie of New Religious Movements; or George
Chryssides' latest book on New Religious Movements.
* The Desecularization of the World: Resurgent Religion and World
Politics by Peter L. Berger, Jonathan Sacks, David Martin, and Tu
Weiming

You can see hard data regarding the number of Hindus in every country
or region in the world, and to see how it is growing, at Adherents.com
:
Hinduism
<http://www.adherents.com/Na/Na_305.html#1873> (please note, that the
page continues).

Adherents.com is a good site, because it states exactly where it got
its information from. However, it should be noted that a movement that
is "neo-Hindu" (that is, doesn't belong to one of the orthodox
branches, but is a Western adaptation) might not in included in
Adherents.com's statistics.

Wikipedia has a page on "Hinduism by Country": 
Hinduism by Country
<http://en.wikipedia.org/wiki/Hinduism_by_country> 
If you click on each country, which has a link, you'd get the article
about Hinduism in that particular country, and the statistics related.
For example:

Hinduism in Canada
<http://en.wikipedia.org/wiki/Hinduism_in_Canada> 

I hope this answers your question. Please contact me if you need any
clarification on this answer before you rate it.

I understand that there is currently a strong movement of lower castes
from Hinduism to a form of Bhuddism
- there was a feature about it on the BBC World Service (radio)