Hi Chiru, 

"Territories" appears to be a field but actually is something else (similar to how Billing / Shipping Address field can't be queried because it really consists of 5 inner fields and how Contact Name = Salutation + First Name + Last Name).

http://www.salesforce.com/us/developer/docs/api/Content/sforce_api_erd_territory.htm

You'll have to query through the sharing table AccountShare, then to Group (of a specific type) and then to Territory.

I don't have an org with Territories enabled handy at the moment to try actual queries but these boards posts might give you some ideas:

http://boards.developerforce.com/t5/Apex-Code-Development/how-do-i-get-the-territory-for-an-account-in-apex-api/td-p/84825

http://boards.developerforce.com/t5/Apex-Code-Development/Query-Account-Territory-help/td-p/197194

RowCause in AccountShare should be 'Territory Management','Territory' or 'Territory Manual', find the group id => go to group definition => find RelatedToId => that'll be the Territory Id. It's messy and you might be able to cut some corners with subqueries/parent queries but the whole setup is painful to retrieve with SOQL...

http://salesforce.stackexchange.com/questions/12460/territories-field-in-account

Regards,
Ashish