I'm alreadu using jquery library on site.
What are pros and cons to use jQuery SWFObject plugin over origional swfobject
jQuery SWFObject plugin
It just removes cross-browser issues out of the mix, it's an abstraction layer. Sometimes declaring the variables right on flash movies are slightly different amongst browsers...better to remove this from the equation, just like you'd use jQuery's .height() instead of figuring out what each browser does yourself.
Do it once, trust that it works, you don't need to load up every browser to test to see that all the variables are right each time (though I'm not saying that's a bad idea).