We'll start the actual Asterisk build by installing DAHDI, since you're probably going to need DAHDI for the line cards that are used with Asterisk. DAHDI supports all of the Digium cards, as well as the Digium clone cards such as OpenVox. And, even if you don't need DAHDI for the hardware that it supports then at least build it for the dummy timer that it supplies.
Incidentally, if you are using any of the Digium clone cards (e.g. OpenVox), you may need to obtain additional source modules for the cards' drivers and insert them into the DAHDI build tree before proceeding with the build. See the appropriate section below, or the manufacturer's install notes, before running the build.
Also, if you need additional help, a fairly complete tutorial on DAHDI can be found at this URL:
http://www.cadvision.com/blanchas/Asterisk/TestingDahdiHW.html
Build DAHDI like this:
cd .../asterisk
tar -xvzf dahdi-linux-complete.tar.gz
cd dahdi-linux-complete
[be sure you've installed any optional, additional echo cancellers]
[be sure you've installed any third party drivers, per their instructions]
make all
su
make install
make config
The last step should install the DAHDI start script, which will cause it to be started by init when the system is booted. You should reboot the system and see that DAHDI does start automatically.
If it doesn't, you can try the following:
su
chkconfig --add dahdi
chkconfig dahdi on
service dahdi start
If the service starts OK now, try rebooting again to make sure that DAHDI comes up at boot time. You may also want to check /var/log/messages to see that DAHDI finds your installed line cards, when it comes up.