Hi,
a series of things were fixed after RC2, especially to gain
Windows compatibility in the new wxpython graphical user interface
which is now included also in the OSGeo4W built.
We'll package GRASS 6.4.0RC3 tomorrow (26 Jan) if there
are no urgent obstacles.
Please complete
http://trac.osgeo.org/grass/wiki/Release/6.4.0RC3-News
Markus