So Im wandering around Soverngard (sp?), and I see Alduin flyover and dissapear. I get done talking to the stormcloak soldier who asks for guidance, and I sprint off and clear the path. All of a sudden Alduin is standing in front me in the middle of the path. I swing my sword and hit him and it brings me into "battle mode". Needless to say I sprinted off to the fotress/castle you have to get to. So this brings me to my question, is it possible then to fight and kill Alduin before you get to the fortress and join the 3 warriors? I didnt want to fight him then because I was afraid of ruining the game or something. Has this happened to anyone else?

You cannot kill him without the other 3 initially. The 4 of you will shout into the mountains and clear up the dense fog. Once that has happened 3 times, then the 4 of you attack Alduin. He dies and disappears, there is nothing to collect. I thought it was a glitch but it is the way it was written.
Bonjoyle

I know what you're getting at, the same thing happened to me. I had a mage, so most my attacks were projectiles. When I got out of the fog I saw him standing directly in front of me, and as he flapped his wings, I started barraging him with lightning. 700 magicka worth only took out a sliver of health, so I thought I was doomed, but those nords just kept on chanting battle-cries while Alduin was flying around in battle speed, not attacking though.

I just hit up Tsun and found my buddies to finish it off, but I was worried that I was about to take on Alduin alone. You cannot, though. You can try your hand at fighting him, but you need the other three to anti-climatically kill him