A decent gaming laptop

Hi guys, right now I have a kind of dectain desktop:

GPU: ATI Radeon 4890
CPU: AMD Phemnom 965
RAM: 2 GB
OS: Windows 7 32bit

Pretty soon I may have to be moving around a lot, and would prefer a laptop, HOWEVER I've had 2 before, and both of them had the EXACT same issue, which was after a few months of owning them, and playing games, I got an issue with the GPU where lines appeared all over the screen (even on the post check, before any software loaded).

I found out at first it was an over heating issue (on an Evesham machine with a dual core centrino processor, 4 gigs of ram and 8600GS graphics card) I then moved onto a Dell machine, it was an Dell XPS M1710. I ensured that I never left my XPS on surfaces where it'll over heat, such as a bed, sofa, or lap. However, same issue occurs.

So now I decided before I go down that road again, and sell my beloved desktop for a gaming laptop, I need some advice as to what gaming laptops are decent, and whether or not it's worth it at all. (maybe notebooks just aren't good for gaming)

My budget would be whatever I sell my Desktop for which would be around £350... I guess.

Thanks