o_O you don't have wget installed???
Sometimes I wonder what Nokia was thinking not having these basic tools pre-installed.

I don't have the incompatible message so it's difficult to debug.
Are you using HAM (Hildon Application Manager; GUI)? If so then yeah it's "incompatible" (not a defined category) but if dpkg is saying it then there are other issues. Did you install libuuid1? Also did you uninstall the Maemo5 version of qemu?

Just to make sure you have the right version of this package, I want you to download this md5sum binary I compiled for Diablo:
Download: http://p7230.homelinux.com/maemo/md5sum
# chmod +x md5sum
# ./md5sum qemu-kvm_0.12.3-0maemo1_armel.deb
Your output should be:
f2ff22cdbbb51c5805aa091de4cdb996 qemu-kvm_0.12.3-0maemo1_armel.deb

If that hash is different then it means you downloaded an older version that I packaged.

If it's the same, then I don't have a clue what the problem is.