SwiftShader 2.0 does successfully emulate VERTEX shader 2.0 as well,
so it's probably your RAM or your CPU's that's insufficient.
The same happened to me when I tried to play Heroes of Might and Magic
V. Menu loads beautifully, but crashes when you try to play the actual
game.
Oblivion without the mod probably used Shader Model 3.0, which is why
both 3dA and SS2.0 failed. 3dA does not properly emulate shaders (it
just tricks the game/software into believing you have them), and SS2.0
only emulates Shader Model 2.1.
Best you get yourself an actual 3D card, or wait patiently until
SwiftShader 3.0 comes out (which will probably be 5 years from now)