Amit:
If you are on F-1 visa status for only one day in 2005, you are technically required to file Form 8843.
That said, the IRS' enforcement of this policy is rather lax, so if you are on F-1 status for less than half of the year, you would file as a resident alien and filing the Form 8843 is no really necessary in the eyes of the IRS because the filing of the resident alien form (Form 1040/1040A/1040EZ) would confirm that you have changed to a different visa, months likely H-1.
If you are on H-1 or H-1B visa in 2006, you will will as a resident alien (Form 1040/1040A/1040EZ) and will not have to file Form 8843 for Tax Year 2006.