In reply to Garbhanach:
"plus one" for premier / aftereffects
yes... you do have to spend a bit of time watching youtube tuturial videos to get the best out of them (probably true of all video editors)
i like creativecow.net as an excellent source of such videos
but they (PP and AE) are fantastic
but i'm going to be annoying and say, you probably want to upgrade your pc/laptop if you are trying to edit HD video on something that has XP on it... remember XP was released more than 10 years ago, a decent new machine will make a massive difference to your workflow... especially with not having to convert the files in the first place but, primarily with rendering out your finished project.