I am on a H1-B with my present company valid from 20th October 2005. Before that I was working on OPT (F-1 visa) from June 30th 2005-19th Oct 2005. I am an Indian citizen. Which form do I use for filing my taxes?

You are not dual status!

File as a non-resident alien, and file either Fprm 1040NR or 1040NR-EZ.