I save a LOT. I'm 18, and I currently have $3200 in savings, and about $1330 in checking, all from part-time jobs. I'm not saying that to brag, but I'm telling you that it CAN be done.
I don't buy stuff that I don't need. Granted, I just purchased a Dell Axim, but I count that as an early birthday present for myself, and I don't plan on making any large purchases in the next few months. The way that I was REALLY inspired to save is by opening a savings account in addition to my checking account. It helps a lot psychologically to squirrel that money away so that it can't be accessed by writing a check or swiping a card.
Basically, evaluate EVERY purchase to determine whether or not you NEED it, or can AFFORD it. If you can comfortably afford it, then great, buy it as a little present for yourself. But if you can't, or if you can wait for something cheaper and better, then save your money.
Trust me, I feel great every time I look at my bank account balance. It feels much better to know you HAVE money than to know you just SPENT it.