Slightly confused by what you mean here...
DWORD is just an unsigned int, with a max of 4294967295
0x######## means that the number is in hexadecimal.
FVF describes what kind of data a vertex contains. To get the FVF value, you 'bitwise inclusive or' different flags together.
The value of the diffuse flag is 0x40, and the value of the specular flag is 0x80.
FVF 338 means that the vertices contain texture, diffuse, normal, and position data.
D3DFVF_TEX1 = 0x0100
D3DFVF_DIFFUSE = 0x0040
D3DFVF_NORMAL = 0x0010
D3DFVF_XYZ = 0x0002
0x0100 | 0x0040 | 0x0010 | 0x0002 = 0x0152 = 338
I do not believe you need to use CONVERT FVF before using any vertex commands, as long as you know what FVF the model is using, and can work with that.
And when specifying a color as a DWORD, it should work like this
0xAARRGGBB
so
0xFFFF0000 is red
0xFF00FF00 is green
0xFF0000FF is blue
0xFF000000 is black
0xFFFFFFFF is white