Source engine to be released before HL2

[Irs2k3]

Well there is two types of Geforce2 MX: 200/400.

I could easily play any game at that time even CS at high detail at 32 bit on a P3, I had the Geforce2 MX 400 !

Of course you need a Geforce3 or any other ~ card that support Vertex and Pixel shaders to see Half-life2 at its best.

[interman]

It's pretty impressive how valve has made such a good LOD system, so you can scale it from a pixel shader 2.0 compliant card, to something like the geforce mx 400. Can't imagine how much extra work that was...

[Irs2k3]

Well Physics in general depends on the CPU, so if you have an old TNT2 card you will still have physics working in the game but you will loose many features like Bump maping, Shaders, Per pixel Lightning, Real time shadows.
From my point of view both the owners of a TNT2 or an R350 will enjoy playing the game and doing cool stuff with physics