Hard Drive, Speakers, and Memory.
Hard Drive - 160GB is a helluva nice amount (I dunno how I'm going to fill up mine) but there comes a time when even thats not enough.
Speakers - Only 2 speakers with sub? You can do better than that, you don't need to right now, but its just a suggestion.
Memory - 1GB won't do, it just won't do. You can play some games at Max, but games like BF2, no way. With the rest of your system, 2GB minimum. I haven't been keeping up, so I don't know why you didn't get 2GB, but you shouldn't even wait if you can afford it.