EMC requires that the Linux kernel be altered so that it has a Real Time patch running within it. This is what makes the machine control run reliably and consistently.
The Real Time patches, prepatched kernels, and modules are available from rtlinux.org http://www.rtlinux.org.
Installing Real Time Linux (RTLinux) seems to be the toughest part to doing an EMC installation. With that said, here are some pages and links designed to help with this.
Tim Goldstein has the essential process for installing RTLinux on RedHat 5.2 http://206.19.206.56/installemc.htm here. If you are looking for the most reliable and easiest to use EMC installation, this is the place to go. This system has been running machines that make production parts for more than a year now.
Ray Henry has written a detailed page on installing RTLinux-2.0 and RTLinux-2.2a on the 2.1.2 distribution. Some have found this helpful for other distributions as well.
Andrew followed the Mandrake install and took notes on his install of rtlinux-2.2 and EMC with a Red Hat 6.1 distribution.
A very recent innovation by the rtlinux organization is the building of RPM packages for some releases of the realtime kernel. These packages install just like any other RPM. They do not provide the source code needed if you will be compiling your own EMC or doing other real time programming that requires compiling.
Good luck!