I fully agree with the above posts, having opted to devote five years of my life, and my wife's, to removing all traces of old paint from our big, old Victorian instead of covering it with plastic. Be prepared for long hours and hard work if you want do do it right (in my opinion, that means getting rid of all the old paint and sanding down the wood until its bright and smooth before priming and painting). It was a kick when someone, having seen the painted front of the house, said the new siding looked nice! That ironic response would never have come if we'd taken the easy route: scraping only the loose paint flakes before painting, Best of luck.
aun@blast.net