This is really a multi-step process:
1) all dependencies need py3k support
2) C code needs to be ported to the py3k interface
3) Python code needs to be checked over, most of it should be fine.
Numpy supports from 1.5
SciPy supports from 0.9.0
matplotlib does not support as of 1.1, "next major release" will support 2.6 or later, and 3.1 or later (no 3.0).
GUI backends for matplotlib: matplotlib supports pyside in git as of July 2011, so support should be in there by the time 3.0 support is.
pyGTK will NEVER have python 3 support, pygobject is required instead. There appears to be some work on matplotlib but it's pretty preliminary.
ffnet has no py3k support
networkx supports py3k
h5py supports py3k
While we're waiting on #1, we can work on #2 and #3 on the modules that do not require matplotlib.