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You don't need it, but it would help a lot, yes. Along with that you should take into consideration other search engine optimization techniques.

A sitemap is definitely beneficial to submit to their webmasters tools.

Any recommendations of creating Sitemap by using any particular website or tool?

http://code.google.com/p/sitemap-generat...Generators

For more information about creating sitemaps read this: http://www.google.com/support/webmasters...wer=183668