Is it possible to replace the back light of the screen

Yes, it’s possible but not easy.
Here’s an example of replacing the backlight lamp.
http://www.laptoprepair101.com/laptop/2007/12/09/replace-laptop-backlight-ccfl-lamp/

My NC6320 screen is constantly distorted and flickering and is aggravated as the screen lid is moved up and down. It started with a vertical line up the screen and got gradually worse. Viewing on an external monitor is however perfect. Is this likely to be a loose connection, a dodgy graphics chip or a problem with the screen itself.

First of all, I don’t think your problem is related to the graphics chip because external video still works fine.
Here’s what you should try:
1. Check connection between the video cable and motherboard. Try reconnecting the cable.
2. Check connection between the video cable and LCD screen. Try reconnecting the cable.
3. If reconnecting the cable doesn’t help, try moving the video cable while the laptop is turned on. If moving the cable affects image on the screen (it’s getting more garbled, getting more lines, or image clears), most likely there is a problem with the video cable. Try replacing it.
4. If moving the cable doesn’t affect image at all but moving the display back and forth affects it, most likely there is a problem with the LCD screen. Try replacing the screen.

Would be grateful for advise before buying any spares.
Thanks

Very handy guide. I do however have a major problem. My cooling fan has stopped working after hearing a little pop and a weird smell. I tried replacing with a new fan but no luck. This may be a problem with the motherboard, if so, what would I need to do to fix the problem and what problem could it be? Thanks

i have a Compaq nc6320 labtop and i need to get my graphics card out.

I believe in this model the graphics card is integrated into the motherboard. The graphics card cannot be removed, replaced, upgraded.
If the graphics card fails, the whole motherboard has to be replaced.
Just in case, check your laptop specs again and make sure you have integrated graphics card.

They go under the computer and you can see where they end up if you turn the laptop around and look where Step 1 is you can actually see the black and white wire.