This is what I found out so far:
General
As for parallel hosting - it's possible (if one wishes to do so).
Google explicitly states that you may host your project simultaneously anywhere else. Sourceforge has nothing in their Terms of Use that would prohibit that either. The licenses that are allowed on both sites would make any restriction void anyway.
From my first impression both seem good. I like google a bit better - w/o being able to actually say why, maybe because it lacks features and looks cleaner 😉
Licenses
Sourceforge accepts OSI compliant licenses
While google code accepts the limited set of licenses shown in the list below. I compiled it here, because it doesn't seem to be available on the net - you'll only see it when setting up a (test-) project.
Google Code - allowed licenses
Apache License 2.0
Artistic License/GPL
Eclipse Public License 1.0
GNU General Public License v2
GNU General Public License v2
GNU Lesser General Public License
MIT License
Mozilla Public License 1.1
New BSD License
I'm thinking of using the LGPL.
Uploading a project/Version Control
For both of them you need to familiarize yourself with using a version control system with which to create the repositories and upload them: CVS or Subversion for sourcforge; Mercurial or Subversion for Google.
I'm going to go with Subversion - the free book for which you find here
Now back to subverting my project...
Bjom