Defense Grid

The minimum code path the game uses is in fact the "low" quality setting where it does as you are suggesting, skipping certain shaders, uses lower resolution textures to help with fill rate, turns many effects off, etc.  What you are likely looking for is a fixed function graphic pipeline and Defense Grid does not have one of those, it is only shader-based.  I'm sorry about that.

Jeff

The situation appears to be very much about the graphics cards.

The Intel GMA950 doesn't have the shader processing power that the HD4850 has. 

The HD4850 has a TeraFlop of shader processing power and a texel fill rate of 25 GTexels/second. 

The GMA950 has about 1/1000th the processing power and 1/25th the fill rate.  Also, it is likely it is using much slower main system memory than it is using dedicated video memory.  That is pretty much what you are seeing about why it is so slow. 

The reason that UT2004 works well with it, is that it has both a fixed-function (non-shader DX7) rendering path and a shader-based path.  Defense Grid only has a DX9 shader-based rendering path (as shader based cards have been common since 2003 and in a title with this size budget one can really only develop one rendering path).

Supporting shader-only rendering obviously wasn't viable when UT2004 was developed so they had to do a fixed function path as well.  Many games released now do a shader-only path.

As for the Turion X2 with a GeForce 9400M, it should work much better on that laptop.  It is about 1/16th as powerful in shader processing and 1/6th as powerful in fill as your HD4850 which is much better obviously than 1/1000th and 1/25th.  Again, if it has dedicated video memory can be a big impact on whether or not the chip can run at full speed on that laptop.

Jeff