Inspiron 1501 - coloured vertical lines down the screen!

I hope someone on here has more of a clue than the so called technical team employed by Dell.

My laptop is relatively new (since August last year), however since Christmas time I have been having issues with it, which I think point to the video card.

On Christmas Day I got a blue screen for all of two seconds, before my laptop shut itself down.  Since then at intermittent intervals I have been having problems with either the screen turning black, bar a square of rainbow coloured lines about a pixel wide, where the mouse pointer was, or alternatively the whole screen is covered in coloured / black lines, about 1cm wide.

I have spoken to technical support on more than one occasion, but despite their running tests, updating the bios file, collecting the laptop, reinstalling the operating system and the video drivers, the problem continues.

Does anyone have any suggestions for what I could do?  All I want is for Dell to collect my laptop and not return it until the problem is resolved, or if they cannot locate the problem, then replace it.  Unfortunately it seems that they are either too cheap, or too incompetent to arrange this for me.  Every time I call them I am forced to run through the story for the umpteenth time, and nobody is taking any ownership for my problem - so frustrated!! 

(PS - wasn't sure if perhaps there was a problem caused by the lack of compatibilty of Windows Vista and the hardware they've used perhaps?  Last time I spoke to someone from Dell, she told me that there was one 'switch' or option that hadn't been activated and that this should stop the problem.  She was going to call me back regarding this but never did)

I suspect that this is perhaps the video card, but am not technical enough to know what to do.  Please help!