First, London, you shouldn't ever reveal your age on the Internet. I am a dad and I know a little something about people who will take advantage of folks because of their age.
Second, for $150US. You could get a new motherboard, a dual core processor, and 2GB of new DDR3 memory. A great source for geek toys in the US is newegg.com.
Here are 3 choices that combined would be less than your budget and would perform quite well with your GPU:http://www.newegg.com/Product/Product.aspx?Item=N82E16813186189http://www.newegg.com/Product/Product.aspx?Item=N82E16820148194http://www.newegg.com/Product/Product.aspx?Item=N82E16819103687
These are just examples of how far you can stretch your budget with a little creativity.
Good luck, young geekling!!! HOOAH!!!