thats from the offical star trek site.

According to Gene Roddenberry in "The Making of Star Trek," stardates were originally created "simply to keep from tying ourselves down to 2265 ... " and to make clear that Star Trek was set in the future. There wasn't a method used to calculate the date, but the producers of the original show did keep a rough track of stardates and there was some logic as to how they progressed. However, as the shows aired out of order from the production order, the stardates would sometimes go backwards. To address this problem, Roddenberry formulated a clever explanation that used a bit of scientific double talk to make stardates sound more plausible, i.e. they "adjust for shifts in relative time which occur due to the vessel's speed and space warp capability ... "
By the time Star Trek: The Next Generation was produced, another digit was added to the stardates. According to Michael and Denise Okuda's "Star Trek Chronology," Gene Roddenberry added the extra digit to show how long had passed between the Original Series and the new show. The first digit used was a 4 and the second digit designated the show's current season. The last three digits before the decimal point would increase from 000-999 according to where in the season the episode took place.

As stardates don't really correspond to anything in reality, fans have taken it upon themselves to come up with their own version of dating based on the standard calendar. By using the year, month, day approach, the day the first episode of Star Trek aired, September 8, 1966, would appear as 6609.08.

They are negative because the zero or starting point seems to the year 2323. So the first two digits in the star date are the number of (star?) years that have elapsed since 2323 (star date 01xx.xx would be one (star?) year since 2323 apparently, etc.)

Interesting. And it's something that someone actually constructed a star date converter and all : )

Why 2323? The year of the first space flight or something?

I knew when I read this that I had to google it. I t always has remained a mystery for me too. So here is what I found out and believe me it was something that I couldn't comprehend completely, so I deferred to putting a link here. Hopefully it explains a little bit.
steve.pugh.net

You can even convert today's dates to the star dates, but somehow they will come out to be negative (I know I was confused too)

"no clue", not on clue...

24th century apparently (saw some quote regarding Q's perception of the 24th century on startrek.com . Yes I googled. again.)

Regarding stardates, I have on clue.
But if it's 07142376, then it's still month/day/year or something like that.

Even if it were made up, I'd be fine with that ;)