Try downloading the source rpm file found here;
http://atrpms.net/dist/fc4/ltmodem/
Make sure you have the kernel source and the kernel development packages as per the installation instructions then try something like;
rpmbuild --recompile --rebuild ltmodem-8.31a10-8.rhfc4.at.src.rpm
cd /usr/src/redhat/RPMS/`uname -i`
rpm -Uvh ltmodem*.rpm