the correct answer is two thousand eight. the word "and" in math (numbers) denotes a decimal. thus two thousand and eight is the number 2000.8 that date would be the year 2000 and 8 tenths of a year. or september 5, 2000. 2000 years plus eight tenths of a year which is 9 months and 5 days.
in addition think of how you should write 2008 on a check or legal document.

PRONUNCING: twenty oh eight is informal and exceptable by todays slang but be it noticed that "oh" is a word not a number. 20 zero eight sounds one syllable too long.