Raising that sort of money when you're 14 is tricky. Minimum wage is well under $10 per hour in your country, so even if you could get a job you'd be looking at working well over 150 hours at $10 an hour to get your $1500. If you did 15 hours a week that's still two and a half months of hard work before you get your computer.
As you're 14, you can't be legally employed so a reliable 15 hour per week job isn't going to happen.
When I was 12 or so I wanted a Gameboy. There were chores around the house to be done and each one had a very small value attached to it - 50 cents for doing this, two dollars to wash dad's truck, 75 cents for something else. The gameboy cost $120 and it took me a month of solid work to earn it.
If you're looking for an easy way to make $1500 I'm sorry to break it to you but it isn't going to happen. There is no 'easy money' in the world. From what I understand, you wouldn't be too keen on doing small jobs for people in your neighborhood (social interaction with strangers scares the monkeys out of me, too) so perhaps you should look for a way to earn that extra cash online.
If you play WoW or SL, you can sell items from the game to other players. Start taking online surveys (they can take a while to build up before you get a cheque, but they're easy as pie - try www.brandinstitute.com, www.cashduck.com). If you have any particular skills with the computer (web design, game skills, hardware help, etc etc) charge people for lessons (you will probably need a paypal account for most of this stuff, have a parent/person over 18 help you set one up if you need to).
Also, keep in mind that there is very little difference between the brand new version of the hardware and last year's model. Often people can't tell the difference if the system is set up correctly, then optimised. If you can save $100 by getting an older model then it's worth your time. Look on ebay and in second hand/pawn shops for cheaper versions of what you want - sometimes people buy the same thing you're looking at buying but then figure out they can't afford it so they sell it to pay the bills. Bargains can be found in lots of places - research and shopping around pays off more often than not.
I'm reminded of a story I heard once about a poor college student who wanted to travel around Europe during his break but couldn't afford the plane ticket. He called the airline and asked if they would give him a free ticket. Of course, the airline said no. So he asked again, would they give him a free ticket IF he could fill a plane with people going to the same place. They told him that if he could fill a whole plane with people who'd paid for their own tickets they'd give him one for free. So that's what he did - he put up notices and arranged people at his campus to go on the same flight, and the airline gave him his free ticket. If you can sell/promote something for a company they'll often reward you. It takes a lot of effort, though.
If you're getting frustrated and are looking at making that money in less than a fortnight and don't mind doing unethical (yet still mostly legal) stuff online to get it, drop me a line.