problem with broadcom NX2

[pinniped <cirilo_bernardo@yahoo.com>]

(quote)
I tries downloading a newer kernel image on another Debian box
...
How do I download the "real" amd64 image?
(end quote)

The package managers will naturally download a file for their own architecture because they download a Packages list for their architecture. Fetch a package with 'wget' (or curl) instead. If the kernel is in the archive list on your AMD64 machine, then do something like:

apt-cache show linux-image-2.6.21-1-amd64 | grep Filename

That should give you most of the path that you will need for 'wget'.  Be very careful with dependencies.

If your AMD64 system doesn't list the package you want, browse the 'pool' directory; the architecture is the last part of the filename (and before .deb).