[2.0] Combining 2 projects

i got two winforms projects separated.
now i need to combine the two projects, just to make it look tidy.

how i do that correctly ?

i tried : Add -> Existing File, and directly select files from other projects.
But i tend to get errors because the namespace is different.
Other error : the data adapter from old project can't be copied into the new project.

Any suggestion ?

actually, i just need to create an mdi window, and from the mdi i need to run the applications from the 2 projects.
how to do that ?
is it possible to gain access to other namespace in other projects, and run it application ?
thx..