Since NoMachine offers packages natively compiled for both 32bit and 64bit architecture, it is strongly suggested you download the package suitable for your architecture.
Nevertheless, it is possible to install a 32bit package on a Linux 64bit system as long as the Operating System offers support for 32bit applications.
For example, in case of Ubuntu 11.10 X86_64, it is necessary to previously install the libc6-i386 and libstdc++6:i386 packages to be able to install NoMachine DEB packages for i386.