I have been compiling the latest SVN on Karmic 64-bit with wxWidgets 2.9.0, which compiles fine on 64-bit. Read build-unix.txt and use the given ../configure parameters on wxWidgets so you can use the makefile.unix.wx2.9 as supplied. (--enable-debug --disable-shared --enable-monolithic)
The download link on the homepage is to the sourceforge tar.gz archive which contains the 32-bit binary and the 0.2.0 sources, which were not yet buildable on 64-bit at the time.
The SVN was first buildable on 64-bit with wx2.9.0 on 28 January 2010.
Hopefully they'll have a wxWidgets 2.9.0 debian package someday.