Graphics / Jumpy DVD / System crashes interrelated?

Hi there I've got big problems. Basically, I've got Windows 2000 Professional and have WinDVD 2.0 and the newest version of InterActual Player. Basically I've gone to dxdiag and have run Test DirectDraw and Test Direct3D. I've got problems seeing the rectangles and also viewing the graphics on the spinning cube.

I've also got a jumpy picture when playing DVD's and the system ALWAYS tends to crash after a period of time (this is also happening sometimes when I'm just using the computer).

My specifications are as follows -

System Model - VT8363
Bios - aNK7VZA Ver 3.2b
DirectX 9.0a(4.09.0000.0901)
I've got Processor: AMD Athlon (tm) Processor, MMX, 3DNOW, ~1.0GHz. (nv4_disp.dll)(5.13.0001.1241)
Also 256 MB RAM
I've got NVIDIA RIVA TNT2 Model 64 / Model 64 Pro, DirectX 9.0 and Screen saver is off, 800x600 pixels.

Please help!