Here are some rough test builds of the new GUI of version 0.43.

GNU/Linux

On GNU/Linux, its easiest to just build it from source. Try using Tcl/Tk 8.5 over 8.4 because the new GUI is fully 8.5 compatible, and 8.5 has a lot of improvements. On Debian/Ubuntu, you can apt-get install tcl8.5 tk8.5.

svn co https://pure-data.svn.sourceforge.net/svnroot/pure-data/branches/pd-gui-rewrite/0.43 pd-gui-rewrite
cd pd-gui-rewrite
./autogen.sh && ./configure && make
cd src 
./pd

Mac OS X/Intel and Windows

There are now nightly builds to download, called Pd-0.43.0-devel:

http://autobuild.puredata.info/auto-build/latest/