To create rpm packages for your system's architecture, you have to download the corresponding .src.rpm files from http://ouaye.net/linknx/src-rpm/
Then you just have to
rpmbuild --rebuild package_name.src.rpm
I only tested it on OpenSuse 10.2 but it should also work on other platforms
The resulting i586 rpm packages for Suse 10.2 can be found in http://ouaye.net/linknx/rpm-i586-suse-10.2/
For Linknx, you can also build the .rpm directly from the .tar.gz file with the following command:
rpmbuild -ta linknx-0.0.1.21.tar.gz