I just picked up SR4 and by default I've been "volunteered" to be the GM. I've selected the setting (Seattle of coarse), made up over a dozen NPCs and a few villians, selected a run (Mission Briefing from the SR website), and have a rough idea of an over all campaign plot in mind. But, I don't know the rules that well (I'm clueless as to how to use the hacking rules). I'm supposed to run next Friday and I think I need help. So please, enlighten me

Just read the rules as much as you can, browse these forums, and check out this site: Shadowrun Resources Aarons got some great stuff on there. I love the Hacker cards and cheat sheets. They are now a main resource for me and my group.