Drawing images with transparency onto a texture?

I'm not sure if I'm going about this properly, but currently I'm painting images on VRAM textures via CopyRect(src_x1, src_y1, width, height, dest_x1, dest_y1, texturebuffer(src_texture), texturebuffer(dest_texture)), using src_textures which are a montage of all the little icons and letters I'll be drawing. CopyRect() seems fast, but it doesn't allow for masking (i.e. where one colour is transparent).

What's the preferred method of doing this...

SetBuffer() and DrawImageRect()?

ReadPixelFast() : if rgb<>0 then WritePixelFast()?

Something else?

Thanks in advance

You might try these from the code archives...

Read and write ARGB by Rob Farley

Alphablitter by WebDext

... unless I am missing the point - does VRAM not support Alpha ??