Megadeth are (still) more interesting to me. Better melodies and solos. It's just that Metallica have some great hits and have become popular that some may pick them. They're kinda repetitive to me, so I vote for Megadeth.
Check the net, I mean yeah even if I wanted to help you, it's pretty obvious that I can't do this in front of all these people :p It depends on how good you are and how protected the lan is. But paying for your own one wouldn't be that much deal for you, since I see that you're already using a computer. It can be not that expensive.