normally you modify your boot logo with a picture, but is there a way to use a short video clip as your boot up logo, i think it would give windows a more "bang" when booting.

can this be done and how?

I have never heard of a way... and I seriously doubt it. Things are very limited when a computer first boots. It would probably not be possible... or if it were then it would probably not be very fast. It would have to load some sort of program to give video... plus it would need to install some sort of graphics driver... codecs... and so on.

not even a flash file, or anything similar?

Considering that the boot screen is there to be something pretty to look at while all the drivers, etc. are being loaded I highly doubt it. why? Well, you'd need to load some drivers to show your video, flash, whatev, and that would defeat the purpose. Also, note that while the boot screen is shown, windows is running in 16-bit color mode. The generic VGA drivers haven't even been loaded yet. I think that's a solid no on that one.

Interesting idea...maybe imposible, but it would be cool.

But what about an exe file? I have used Bink&Smacker to convert some videos to executable files and run these during windows setup.