Hello I tried to install the newest reiserfstools on a pure x86_64 linux 2.6.18 system. The 64bit were not the problem but linux 2.6.18 has introduced 'make headers_install' and the header 'asm/unaligned.h' is not installed by this. I got reiserfstools working via CFLAGS to the linux source but you should possibly update reiserfstools to reflect this change in strategy in the linux configuration system.
Regards, Dennis
