How to create one bitmap from two?

Hello,

I have a problem, because I'd like to join two bitmaps in order to get one ... I don't know how to do it in .NET CF.

for e.g. :
Bitmap b1 = ... // size(256,256)
Bitmap b2 = ... // size(256,256)

// joining

Bitmap b3 = ... // size(512,256)

Does anyone know how to do that?