Hi Arun,
I'd be happy to assist you to the best of my ability
considering I struggled getting feedback on dataservices in this
forum myself. "Flex Data Services" no longer exists. It is now
Blazeds (
http://opensource.adobe.com/wiki/display/blazeds/BlazeDS). Flex Builder 3.0 is just an IDE, which you don't necessarily
need(a regular text editor will do), but you will need however the
flex 3 sdk to compile your work. I had a lot of trouble trying to
use flex 2 code for flex data services with the new flex 3 and the
old flex data services, so be cautious with that(I never
succeeded). Hope that helps!