glBegin questions

Use glClientActiveTexture to set the active (client) texture unit and then set the pointer for that unit.

As for interleaved arrays, that's really just a waste of time. Just use the appropriate gl*Pointer functions. At least that way you decide how to structure your data instead of following the specific formats glInterleavedArrays provides.

E.g.

Local tc:Byte Ptr ' the data -- in the case of a vbo, this would remain Null
' for the sake of example, the data is arranged as such: uv0, uv1, uv0, uv1
' where uv are the respective components and the number is the channel
' you'll probably want to organize your data so that it's all lumped together contiguously
' which would basically look like u0v0, u0v0, u0v0, u0v0, u1v1, u1v1, u1v1, u1v1 where each channel has
' a stride of 0 (is tightly packed) and it is only necessary to point to the appropriate offset into the data

glClientActiveTexture( GL_TEXTURE0 ) ' set the unit
glEnableClientState( GL_TEXTURE_COORD_ARRAY ) ' enable the texcoord pointer for this unit
glTexCoordPointer( 2, GL_FLOAT, 8, tc ) ' set the pointer
' stride is set to 8 so it skips over channel 1 and uses only channel 0

' repeat for the next unit
glClientActiveTexture( GL_TEXTURE1 )
glEnableClientState( GL_TEXTURE_COORD_ARRAY )
glTexCoordPointer( 2, GL_FLOAT, 8, tc+8 ) ' set it to use the second set of texture coordinates

This is a snippet from my engine's material code, basically shows how I handle the data.

If _maps.Count( ) = 0 And _class <> TEX_TARGET Then
    Return 0
EndIf
' set unit
ActiveTexture( unit )
ClientActiveTexture( unit )

' attempt to get a texture
Local tex:ITexture
Try
    tex = ITexture(_maps.ValueAtIndex( Floor((time * animspeed) Mod _maps.Count( )) ))
Catch o:Object
    tex = Null
End Try
 
' offset into the data that the texture coordinates start at
Local off%=0
' you know, this would be a lot easier if i had a ternary operator
Select textype
    Case GL_FLOAT, GL_INT
        off = texoff+(4*texSize)*_tcSet
    Case GL_DOUBLE
        off = texoff+(8*texSize)*_tcSet
    Case GL_SHORT
        off = texoff+(2*texSize)*_tcSet
    Default
        If Not (_class&9) Then
            Return 0
        EndIf
End Select

Select _class
    Case TEX_NORMAL
        If Not tex Then Return 0
        tex.Bind( unit ) ' set unit & bind texture
        
        ' disable coordinate generation
        glDisable( GL_TEXTURE_GEN_S )
        glDisable( GL_TEXTURE_GEN_T )
        
        EnableClientTextureArray( unit )
        glTexCoordPointer( texsize, textype, stride, texp+off )
        
        MatrixMode( GL_TEXTURE )
        glLoadIdentity( )
        For Local i:Int = 0 To _tcmods.Length-1
            If _tcmods[i] Then _tcmods[i].Do( time, tex.ow, tex.oh )
        Next