I'm about to play in a tounament in NZ, how do I look up my opponents' games to prepare for them? Since my ratings 1574 i won't be playing GMs or anyone like that. Is there a big file out there somewhere on the internet with lots of master and non-master games which I can download?

I use this site to look up tons of games. This site is ordered by different openings.    

http://www.chessopolis.com/chessfiles/pgn_openings.htm

Good Luck!

What you do is you click on your opponents name and (if necessary) then click online chess. This will take you to a list of his games as well as the same stats you can view on your own profile. Browse at your own leisure.

I don't mean on Chess.com, I mean a real over-the-board tournament, and when the pairings get put up, I can look up any of my opponents games on the internet, to see what openings they play. Can this be done for free? Or do I need to buy one of those databases with 5 million games or so in it?

I found this:

http://www.poisonpawn.co.nz/nzgames.zip

You can extract pgn files, open them with Notepad, Wordpad, etc. and look for the person you are interested in.

I might be saying something silly here but it would be worth to look in local chess clubs websites, to see if they have any old tournament games available online, as chess players of that level don't normally travel long distances to play tournaments!