It's kinda sad that, like with a .swf loop that I made, this isn't gonna get a lot of high marks. However, I have learned from my blamming that post production shit shouldn't be released before project complation. This is a site where users can express themselves through art. Sadly, this is not a finished piece so it cannot truly be considered art, however has potential to be art, like the sketch that it is. I would recommend you use places like tumblr to post WIP's and a means to update future follower. But Yeh... I like the animation. You've definitely studied the stances and movements well. He does seem to be swinging his sword very close to his body and does seem a bit strange (however, when you colour it in it may over come this).
So sadly I only give it a 1.5 as you also need to learn this lesson.
However I would love to see future work from you (I would consider creating drawings before making animations to improve your art style and your understanding of stances).

But yeh...

Well done and good luck with future projects...

The animation is pretty fluent!

Nice start. As a bad drawer who likes to give his poor opinion on everything, I would say its too bad the details disappear after few frames, and in the last frames, the right arms is in a really wierd position, it should be horizontal, and the left one vetical (try it yourself :P).

looks grate you should continue

Ooookay.
First of, the whole movement is weird. He switches from righty to lefty right at the last instant for no aparent reason. It sure looks like you did your research, though.
I know samurais are supposed to be stiff, but some anticipations to certain movements would help, specially the down slash, otherwise his weapon would seem weightless.
Nice work on the rebound of the sword right at the last 4 frames or so.
You nailed it at the timing, if he didn't look like a samurai, people would still recognize him as one.
Flash has a feature called onion skin (I think), it helps you see a transparent fersion of the previous frames, just like in traditional work, look it up, that would help you avoid shifting in position and deformations on the character.
All and all, it's still pretty impressive for someone who has been using flash for a month, just keep up the good work, I think you've got what it takes to be an animator.

Hope I didn't sound too much of a hardass. Cheers!