Possible display/graphics problem

I bought my 15'' Macbook Pro at towards the end of October last year (so the warranty's just run out. Yay...) and I think it may be developing a problem with its display or graphics card. This is my first Mac and my first real problem with it so I'm not sure what information to provide so if you want to know something that I've not written here just ask.

It started last Friday when I thought two or three times that I caught some weird distortion on my screen out of the corner of my eye. I though nothing of it and kept using it. On Saturday I used it for about and hour and everything seemed fine but yesterday, after only being turned on for less than 5 minutes, my whole screen went weird. The colours went odd and pink vertical lines were all over the screen. I'm a bit jumpy when it comes to computer problems and such so I closed the lid in a panic, and when I opened it up the display was still weird but went back to normal after a couple of seconds. I kept using it for just over an hour when the same thing happened again, except this time the lines on the screen were blue and the screen went back to normal by itself after a couple of seconds.

As far as I can tell everything else is working fine and so far the problem has only happened very occasionally - I'm typing this on the Macbook in question and it's behaved fine so far for the hour or so that I've had it on. Can anyone offer any advice?

Here's the specs on my Macbook, in case you need them:
Macbook Pro 15''
OS X 10.6.6
2.4GHz Intel Core i5
4GB RAM
Intel HD Graphics GPU Built-in
NVIDIA GeForce GT 330M PCIe (I'm afraid I don't know what that means or which one it's using - I'm quite a noob when it comes to graphics!)

 

Which chip is that, the Intel or the Nvidia? And is there any way to get it to only use the one which doesn't have a problem? I don't even know if that's possible but if it is it would be good for me as I can't really afford to pay for a repair right now.