I didn't plan on writing this review, but I see people are having trouble with the whole code thing. If you go into the folder the game is installed in (I think the default is documents/gamefly/games/Uplink, or something like that), there should be a pdf file that is called Uplink manual. If you open that up and scroll down, you'll see the codes it's talking about.
Now for the actual review of the game. There is a bit of a learning curve, which isn't helped by the poor tutorial, which stopped working for me halfway through. I also had some issues with changing the resolution, it only seemed to like the lowest option, which was 640x480. The missions that you get in the game can also be challenging because at first there is a real lack of direction, there have been a few times when I had to look online to see what it was I had to do. But once you figure the game out is when it starts getting fun, it just takes some patience.