You should use Adobe Flash, it would be better to let someone else make it rather than yourself since you are a beginner. Just post it in the marketplace.
Whether you let someone do it for you or you do it yourself, always include a skip button in html.
Some dont have flash, or some have slow connections, others just don't want to wait for it to finish playing.
I use Adobe Flash, but I can't make anything very advanced with it.
I made a logo with waves coming out of it and thats about it.
Flash intros aren't really a good idea, and flash doesn't work so well in some broswers.
However you can make a free flash intro easy at freeflashbuilder.com